delivered the opinion of the Court.

The appellant, Abdiel Caban, challenges the constitutionality of § 111 of the New York Domestic Relations Law (Mc*382Kinney 1977), under which two of his natural children were adopted by their natural mother and stepfather without his consent. We find the statute to be unconstitutional, as the distinction it invariably makes between the rights of unmarried mothers and the rights of unmarried fathers has not been shown to be substantially related to an important state interest.

I

Abdiel Caban and appellee Maria Mohammed lived together in New York City from September 1968 until the end of 1973. During this time Caban and Mohammed represented themselves as being husband and wife, although they never legally married. Indeed, until 1974 Caban was married to another woman, from whom he was separated. While living with the appellant, Mohammed gave birth to two children: David Andrew Caban, born July 16, 1969, and Denise Caban, born March 12, 1971. Abdiel Caban was identified as the father on each child’s birth certificate, and lived with the children as their father until the end of 1973. Together with Mohammed, he contributed to the support of the family.

In December 1973, Mohammed took the two children and left the appellant to take up residence with appellee Kazin Mohammed, whom she married on January 30, 1974. For the next nine months, she took David and Denise each weekend to visit her mother, Delores Gonzales, who lived one floor above Caban. Because of his friendship with Gonzales, Caban was able to see the children each week when they came to visit their grandmother.

In September 1974, Gonzales left New York to take up residence in her native Puerto Rico. At the Mohammeds’ request, the grandmother took David and Denise with her. According to appellees, they planned to join the children in Puerto Rico as soon as they had saved enough money to start a business there. During the children’s stay with their grandmother, Mrs. Mohammed kept in touch with David and *383Denise by mail; Caban communicated with the children through his parents, who also resided in Puerto Rico. In November 1975, he went to Puerto Rico, where Gonzales willingly surrendered the children to Caban with the understanding that they would be returned after a few days. Caban, however, returned to New York with the children. When Mrs. Mohammed learned that the children were in Caban’s custody, she attempted to retrieve them with the aid of a police officer. After this attempt failed, the appellees instituted custody proceedings in the New York Family Court, which placed the children in the temporary custody of the Mohammeds and gave Caban and his new wife, Nina, visiting rights.

In January 1976, appellees filed a petition under § 110 of the New York Domestic Relations Law to adopt David and Denise.1 In March, the Cabans cross petitioned for adoption. After the Family Court stayed the custody suit pending the outcome of the adoption proceedings, a hearing was held on the petition and cross-petition before a Law Assistant to a New York Surrogate in Kings County, N. Y. At this hearing, both the Mohammeds and the Cabans were represented by counsel and were permitted to present and cross-examine witnesses.

The Surrogate granted the Mohammeds’ petition to adopt the children, thereby cutting off all of appellant’s parental *384rights and obligations.2 In his opinion, the Surrogate noted the limited right under New York law of unwed fathers in adoption proceedings: “Although a putative father’s consent to such an adoption is not a legal necessity, he is entitled to an opportunity to be heard in opposition to the proposed stepfather adoption.” Moreover, the court stated that the appellant was foreclosed from adopting David and Denise, as the natural mother had withheld her consent. Thus, the court considered the evidence presented by the Cabans only insofar as it reflected upon the Mohammeds’ qualifications as prospective parents. The Surrogate found them well qualified and granted their adoption petition.

The New York Supreme Court, Appellate Division, affirmed. It stated that appellant’s constitutional challenge to § 111 was foreclosed by the New York Court of Appeals’ decision in In re Malpica-Orsini, 36 N. Y. 2d 568, 331 N. E. 2d 486 (1975), appeal dism’d for want of substantial federal question sub nom. Orsini v. Blasi, 423 U. S. 1042 (1976). In re David Andrew C., 56 App. Div. 2d 627, 391 N. Y. S. 2d 846 (1977). The New York Court of Appeals dismissed the appeal in a *385memorandum decision based on In re Malpica-Orsini, supra. In re David A. C., 43 N. Y. 2d 708, 372 N. E. 2d 42 (1977).

On appeal to this Court, appellant presses two claims. First, he argues that the distinction drawn under New York law between the adoption rights of an unwed father and those of other parents violates the Equal Protection Clause of the Fourteenth Amendment. Second, appellant contends that this Court’s decision in Quilloin v. Walcott, 434 U. S. 246 (1978), recognized the due process right of natural fathers to maintain a parental relationship with their children absent a finding that they are unfit as parents.3

II

Section 111 of the N. Y. Dom. Rel. Law (McKinney 1977) provides in part that

“consent to adoption shall be required as follows: . . . (b) Of the parents or surviving parent, whether adult or infant, of a child born in wedlock; [and] (c) Of the mother, whether adult or infant, of a child bom out of wedlock. . .

The statute makes parental consent unnecessary, however, in certain cases, including those where the parent has abandoned or relinquished his of her rights in the child or has been adjudicated incompetent to care for the child.4 Absent one of *386these circumstances, an unwed mother has the authority under New York law to block the adoption of her child simply by withholding consent. The unwed father has no similar control *387over the fate of his child, even when his parental relationship is substantial — as in this case. He may prevent the termination of his parental rights only by showing that the best interests of the child would not permit the child’s adoption by the petitioning couple.

Despite the plain wording of the statute, appellees argue that unwed fathers are not treated differently under § 111 from other parents. According to appellees, the consent requirement of § 111 is merely a formal requirement, lacking in substance, as New York courts find consent to be unnecessary whenever the best interests of the child support the adoption. Because the best interests of the child always determine whether an adoption petition is granted in New York, appellees contend that all parents, including unwed fathers, are subject to the same standard.

Appellees’ interpretation of § 111 finds no support in New York case law. On the contrary, the New York Court of Appeals has stated unequivocally that the question whether consent is required is entirely separate from that of the best interests of the child.5 Indeed, the Surrogate’s decision in the present case, affirmed by the New York Court of Appeals, was *388based upon the assumption that there was a distinctive difference between the rights of Abdiel Caban, as the unwed father of David and Denise, and Maria Mohammed, as the unwed mother of the children: Adoption by Abdiel was held to be impermissible in the absence of Maria’s consent, whereas adoption by Maria could be prevented by Abdiel only if he could show that the Mohammeds’ adoption of the children would not be in the children’s best interests. Accordingly, it is clear that § 111 treats unmarried parents differently according to their sex.6

III

Gender-based distinctions “must serve important governmental objectives and must be substantially related to achievement of those objectives” in order to withstand judicial scrutiny under the Equal Protection Clause. Craig v. Boren, 429 U. S. 190, 197 (1976). See also Reed v. Reed, 404 U. S. 71 (1971). The question before us, therefore, is whether the distinction in § 111 between unmarried mothers and unmarried fathers bears a substantial relation to some important state interest. Appellees assert that the distinction is justified by a fundamental difference between maternal and paternal relations — that “a natural mother, absent special circumstances, bears a closer relationship with her child . . . than a father does.” Tr. of Oral Arg. 41.

*389Contrary to appellees’ argument and to the apparent presumption underlying § 111, maternal and paternal roles are not invariably different in importance. Even if unwed mothers as a class were closer than unwed fathers to their newborn infants, this generalization concerning parent-child relations would become less acceptable as a basis for legislative distinctions as the age of the child increased. The present case demonstrates that an unwed father may have a relationship with his children fully comparable to that of the mother. Appellant Caban, appellee Maria Mohammed, and their two children lived together as a natural family for several years. As members of this family, both mother and father participated in the care and support of their children.7 There is no reason to believe that the Caban children — aged 4 and 6 at the time of the adoption proceedings — had a relationship with their mother unrivaled by the affection and concern of their father. We reject, therefore, the claim that the broad, gender-based distinction of § 111 is required by any universal difference between maternal and paternal relations at every phase of a child’s development.

As an alternative justification for § 111, appellees argue that the distinction between unwed fathers and unwed mothers is substantially related to the State’s interest in promoting the adoption of illegitimate children. Although the legislative *390history of § 111 is sparse,8 in In re Malpica-Orsini, 36 N. Y. 2d 568, 331 N. E. 2d 486 (1975), the New York Court of Appeals identified as the legislature’s purpose in enacting § 111 the furthering of the interests of illegitimate children, for whom adoption often is the best course.9 The court concluded:

“To require the consent of fathers of children born out of wedlock ... , or even some of them, would have the overall effect of denying homes to the homeless and of depriving innocent children of the other blessings of adoption. The cruel and undeserved out-of-wedlock stigma would continue its visitations. At the very least, the worthy process of adoption would be severely impeded.” 36 N. Y. 2d, at 572, 331 N. E. 2d, at 489.

The court reasoned that people wishing tO' adopt a child born out of wedlock would be discouraged if the natural father could prevent the adoption by the mere withholding of his consent. Indeed, the court went so far as to suggest that “[m]arriages would be discouraged because of the reluctance of prospective husbands to involve themselves in a family sit*391uation where they might only be a foster parent and could not adopt the mother's offspring.” Id., at 573, 331 N. E. 2d, at 490. Finally, the court noted that if unwed fathers’ consent were required before adoption could take place, in many instances the adoption would have to be delayed or eliminated altogether, because of the unavailability of the natural father.10

The State’s interest in providing for the well-being of illegitimate children is an important one. We do not question that the best interests of such children often may require their adoption into new families who will give them the stability of a normal, two-parent home. Moreover, adoption will remove the stigma under which illegitimate children suffer. But the unquestioned right of the State to further these desirable ends by legislation is not in itself sufficient to justify the gender-based distinction of § 111. Rather, under the relevant cases applying the Equal Protection Clause it must be shown that the distinction is structured reasonably to further these ends. As we repeated in Reed v. Reed, 404 U. S., at 76, such a statutory “classification 'must be reasonable, not arbitrary, and must rest upon some ground of difference having a fair and substantial relation to the object of the legislation, so that all persons similarly circumstanced shall be treated alike.’ Royster Guano Co. v. Virginia, 253 U. S. 412, 415 (1920).”

We find that the distinction in § 111 between unmarried mothers and unmarried fathers, as illustrated by this case, does not bear a substantial relation to the State’s interest in providing adoptive homes for its illegitimate children. It may be that, given the opportunity, some unwed fathers would prevent the adoption of their illegitimate children. This impediment to adoption usually is the result of a natural *392parental interest shared by both genders alike; it is not a manifestation of any profound difference between the affection and concern of mothers and fathers for their children. Neither the State nor the appellees have argued that unwed fathers are more likely to object to the adoption of their children than are unwed mothers; nor is there any self-evident reason why as a class they would be.

The New York Court of Appeals in In re Malpica-Orsini, supra, suggested that the requiring of unmarried fathers’ consent for adoption would pose a strong impediment for adoption because often it is impossible to locate unwed fathers when adoption proceedings are brought, whereas mothers are more likely to remain with their children. Even if the special difficulties attendant upon locating and identifying unwed fathers at birth would justify a legislative distinction between mothers and fathers of newborns,11 these difficulties need not persist past infancy. When the adoption of an older child is sought, the State’s interest in proceeding with adoption cases can be protected by means that do not draw such an inflexible gender-based distinction as that made in § 111.12 In those cases where the father never has come forward to participate in the rearing of his child, nothing in the Equal Protection Clause precludes the State from withholding from him the privilege of vetoing the adoption of that child. Indeed, under the statute as it now stands the surrogate may proceed in the absence of consent when the parent whose consent otherwise would be required never has come forward or has abandoned the child.13 See, e. g., In re Orlando F., 40 N. Y. 2d 103, 351 *393N. E. 2d 711 (1976). But in cases such as this, where the father has established a substantial relationship with the child and has admitted his paternity,14 a State should have no difficulty in identifying the father even of children born out of wedlock.15 Thus, no showing has been made that the different treatment afforded unmarried fathers and unmarried mothers under § 111 bears a substantial relationship to the proclaimed interest of the State in promoting the adoption of illegitimate children.

*394In sum, we believe that § 111 is another example of “over-broad generalizations” in gender-based classifications. See Califano v. Goldfarb, 430 U. S. 199, 211 (1977); Stanton v. Stanton, 421 U. S. 7, 14-15.(1975). The effect of New York’s classification is to discriminate against unwed fathers even when their identity is known and they have manifested a significant paternal interest in the child. The facts of this case illustrate the harshness of classifying unwed fathers as being invariably less qualified and entitled than mothers to exercise a concerned judgment as to the fate of their children. Section 111 both excludes some loving fathers from full participation in the decision whether their children will be adopted and, at the same time, enables some alienated mothers arbitrarily to cut off the paternal rights of fathers. We conclude that this undifferentiated distinction between unwed mothers and unwed fathers, applicable in all circumstances where adoption of a child of theirs is at issue, does not bear a substantial relationship to the State’s asserted interests.16

The judgment of the New York Court of Appeals is

Reversed.

dissenting.

For reasons similar to those expressed in the dissenting opinion of Mr. Justice Stevens, I agree that § 111 (1)(c) of *395the New York Domestic Relations Law (McKinney 1977) is not constitutionally infirm. The State's interest in promoting the welfare of illegitimate children is of far greater importance than the opinion of the Court would suggest. Unlike the children of married parents, illegitimate children begin life with formidable handicaps. They typically depend upon the care and economic support of only one parent — usually the mother. And, even in this era of changing mores, they still may face substantial obstacles simply because they are illegitimate. Adoption provides perhaps the most generally available way of removing these handicaps. See H. Clark, Law of Domestic Relations 177 (1968). Most significantly, it provides a means by which an illegitimate child can become legitimate — a fact that the Court’s opinion today barely acknowledges.

The New York statute reflects the judgment that, to facilitate this ameliorative change in the child’s status, the consent of only one parent should ordinarily be required for adoption of a child born out of wedlock. The mother has been chosen as the parent whose consent is indispensable. A different choice would defy common sense. But the unwed father, if he is the lawful custodian of the child, must under the statute also consent.* And, even when he does not have custody, the unwed father who has an established relationship with his illegitimate child is not denied the opportunity to participate in the adoption proceeding. His relationship with the child will be terminated through adoption only if a court determines that adoption will serve the child’s best interest. These distinctions represent, I think, a careful accommodation of the competing interests at stake and bear a close and substantial relátionship to the State’s goal of promoting the welfare of its children. In my view, the Constitution requires no more.

The appellant has argued that the statute, in granting *396rights to an unwed mother that it does not grant to an unwed father, violates the Equal Protection Clause by discriminating on the basis of gender. And he also has made the argument that the statute, because it withholds from the unwed father substantive rights granted to all other classes of parents, violates both the Equal Protection Clause and the Due Process Clause of the Fourteenth Amendment. I find the latter contention less troublesome than does my Brother Stevens, and see no ultimate merit in the former.

A

The appellant relies primarily on Stanley v. Illinois, 405 U. S. 645, in advancing the second argument identified above. But it is obvious that the principle established in that case is not offended by the New York law. The Illinois statute invalidated in Stanley employed a stark and absolute presumption that the unwed father was not a fit parent. Upon the death of the unwed mother, the children were declared wards of the State and in Stanley’s case were removed from his custody without any hearing or demonstration that he was not a fit parent. Custody having been taken from the father by a stranger — the State — the children were then transferred to other strangers. Stanley, who had lived with his three children over a period of 18 years, was given no opportunity to object. And, although the statute purported to promote the welfare of illegitimate children, the State’s termination of Stanley’s family relationship was made without any finding that the interests of his children would thereby be served.

Here, in sharp contrast, the unwed mother is alive, has married, and has voluntarily initiated the adoption proceeding. The appellant has been given the opportunity to participate and to present evidence on the question whether adoption would be in the best interests of the children. Thus, New York has accorded to the appellant all the process that Illinois unconstitutionally denied to Stanley.

*397The Constitution does not require that an unmarried father’s substantive parental rights must always be coextensive with those afforded to the fathers of legitimate children. In this setting, it is plain that the absence of a legal tie with the mother provides a constitutionally valid ground for distinction. The decision to withhold from the unwed father the power to veto an adoption by the natural mother and her husband may well reflect a judgment that the putative father should not be able arbitrarily to withhold the benefit of legitimacy from his children.

Even if it be assumed that each married parent after divorce has some substantive due process right to maintain his or her parental relationship, cf. Smith v. Organization of Foster Families, 431 U. S. 816, 862-863 (opinion concurring in judgment), it by no means follows that each unwed parent has any such right. Parental rights do not spring full-blown from the biological connection between parent and child. They require relationships more enduring. The mother carries and bears the child, and in this sense her parental relationship is clear. The validity of the father’s parental claims must be gauged by other measures. By tradition, the primary measure has been the legitimate familial relationship he creates with the child by marriage with the mother. By definition, the question before us can arise only when no such marriage has taken place. In some circumstances the actual relationship between father and child may suffice to create in the unwed father parental interests comparable to those of the married father. Cf. Stanley v. Illinois, supra. But here we are concerned with the rights the unwed father may have when his wishes and those of the mother are in conflict, and the child’s best interests are served by a resolution in favor of the mother. It seems to me that the absence of a legal tie with the mother may in such circumstances appropriately place a limit on whatever substantive constitutional claims might otherwise exist by virtue of the father’s actual relationship with the children.

*398B

The appellant’s equal protection challenge to the distinction drawn between the unwed father and mother seems to me more substantial. Gender, like race, is a highly visiblé and immutable characteristic that has historically been the touchstone for pervasive but often subtle discrimination. Although the analogy to race is not perfect and the constitutional inquiry therefore somewhat different, gender-based statutory classifications deserve careful constitutional examination because they may reflect or operate to perpetuate mythical or stereotyped assumptions about the proper roles and the relative capabilities of men and women that are unrelated to any inherent differences between the sexes. Cf. Orr v. Orr, 440 U. S. 268. Sex-based classifications are in many settings invidious because they relegate a person to the place set aside for the group on the basis of an attribute that the person cannot change. Reed v. Reed, 404 U. S. 71; Stanton v. Stanton, 421 U. S. 7; Frontiero v. Richardson, 411 U. S. 677; Weinberger v. Wiesenfeld, 420 U. S. 636; Orr v. Orr, supra. Such laws cannot be defended, as can the bulk of the classifications that fill the statute books, simply on the ground that the generalizations they reflect may be true of the majority of members of the class, for a gender-based classification need not ring false to work a discrimination that in the individual case might be invidious. Nonetheless, gender-based classifications are not invariably invalid. When men and women are not in fact similarly situated in the area covered by the legislation in question, the Equal Protection Clause is not violated. See, e. g., Schlesinger v. Ballard, 419 U. S. 498. Cf. San Antonio Independent School Dist. v. Rodriguez, 411 U. S. 1, 59 (concurring opinion).

In my view, the gender-based distinction drawn by New York falls in this latter category. With respect to a large group of adoptions — those of newborn children and infants— unwed mothers and unwed fathers are simply not similarly *399situated, as my Brother Stevens has demonstrated. Our law has given the unwed mother the custody of her illegitimate children precisely because it is she who bears the child and because the vast majority of unwed fathers have been unknown, unavailable, or simply uninterested. See H. Clark, Law of Domestic Relations 176-177 (1968); H. Krause, Illegitimacy: Law and Social Policy 29-32 (1971). This custodial preference has carried with it a correlative power in the mother to place her child for adoption or not to do so.

The majority of the States have incorporated these basic common-law rules in their statutes identifying the persons whose participation or consent is requisite to a valid adoption. See generally Note, 59 Va. L. Rev. 517 (1973); Comment, 70 Mich. L. Rev. 1581 (1972). These common-law and statutory rules of law reflect the physical reality that only the mother carries and gives birth to the child, as well as the undeniable social reality that the unwed mother is always an identifiable parent and the custodian of the child — until or unless the State intervenes. The biological father, unless he has established a familial tie with the child by marrying the mother, is often a total stranger from the State’s point of view. I do not understand the Court to question these pragmatic differences. See ante, at 392. An unwed father who has not come forward and who has established no relationship with the child is plainly not in a situation similar to the mother’s. New York’s consent distinctions have clearly been made on this basis, and in my view they do not violate the Equal Protection Clause of the Fourteenth Amendment. See Schlesinger v. Ballard, supra.

In this case, of course, we are concerned not with an unwilling or unidentified father but instead with an unwed father who has established a paternal relationship with his children. He is thus similarly situated to the mother, and his claim is that he thus has parental interests no less deserving of protection than those of the mother. His contention that the New York *400law in question consequently discriminates against him on the basis of gender cannot be lightly dismissed. For substantially the reasons expressed by Mr. Justice Stevens in his dissenting opinion, post, at 412-413, I believe, however, that this gender-based distinction does not violate the Equal Protection Clause as applied in the circumstances of the present case.

It must be remembered that here there are not two, but three interests at stake: the mother’s, the father’s, and the children’s. Concerns humane as well as practical abundantly support New York’s provision that only one parent need consent to the adoption of an illegitimate child, though it requires both parents to consent to the adoption of one already legitimate. If the consent of both unwed parents were required, and one withheld that consent, the illegitimate child would remain illegitimate. Viewed in these terms the statute does not in any sense discriminate on the basis of sex. The question, then, is whether the decision to select the unwed mother as the parent entitled to give or withhold consent and to apply that rule even when the unwed father in fact has a paternal relationship with his children constitutes invidious sex-based discrimination.

The appellant’s argument would be a powerful one were this an instance in which it had been found that adoption by the father would serve the best interests of the children, and in the face of that finding the mother had been permitted to block the adoption. But this is not such a case. As my Brother Stevens has observed, under a sex-neutral rule — assuming that New York is free to require the consent of but one parent for the adoption of an illegitimate child — the outcome in this case would have been the same. The appellant has been given the opportunity to show that an adoption would not be in his children’s best interests. Implicit in the finding made by the New York courts is the judgment that termination of his relationship with the children will in fact promote their well-being — a judgment we are obligated to accept.

*401That the statute might permit — in a different context — the unwed mother arbitrarily to thwart the wishes of the caring father as well as the best interests of the child is not a sufficient reason to invalidate it as applied in the present case. For here the legislative goal of the statute — to facilitate adoptions that are in the best interests of illegitimate children after consideration of all other interests involved — has indeed been fully and fairly served by this gender-based classification. Unless the decision to require the consent of only one parent is in itself constitutionally defective, which nobody has argued, the same interests that support that decision are sufficiently profound to overcome the appellant’s claim that he has been invidiously discriminated against, because he is a male.

I agree that retroactive application of the Court’s decision today would work untold harm, and I fully subscribe to Part III of Mr. Justice Stevens’ dissent.

Under § 111 (l)(c) of the New York Domestic Relations Law (McKinney 1977), the adoption of a child born out of wedlock usually requires the consent of the natural mother; it does not require that of the natural father unless he has “lawful custody.” See ante, at 386 n. 4. Appellant, the natural but noncustodial father of two school-age children born out of wedlock,1 challenges that provision insofar as it allows the adoption of his natural children by the husband of the natural mother without his consent. Appellant’s primary objection is that this unconsented-to termination of his parental rights without proof of unfitness on his part violates the substantive component of the Due Process Clause of the Fourteenth Amendment. Secondarily, he attacks § 111 (l)(c)’sdis-*402parate treatment of natural mothers and natural fathers as a violation of the Equal Protection Clause of the same Amendment. In view of the Court’s disposition, I shall discuss the equal protection question before commenting on appellant’s primary contention. I shall then indicate why I think the holding of the Court, although erroneous, is of limited effect.

I

This case concerns the validity of rules affecting the status of the thousands of children who are born out of wedlock every day.2 All of these children have an interest in acquiring the status of legitimacy; a great many of them have an interest in being adopted by parents who can give them opportunities that would otherwise be denied; for some the basic necessities of life are at stake. The state interest in facilitating adoption in appropriate cases is strong — perhaps even “compelling.” 3

*403Nevertheless, it is also true that § 111 (l)(c) gives rights to natural mothers that it withholds from natural fathers. Because it draws this gender-based4 distinction between two classes of citizens who have an equal right to fair and impartial treatment by their government, it is necessary to determine whether there are differences between the members of the two classes that provide a justification for treating them differently.5 That determination requires more than merely recognizing that society has traditionally treated the two classes differently.6 But it also requires analysis that goes beyond a merely reflexive rejection of gender-based distinctions.

*404Men and women are different, and the difference is relevant to the question whether the mother may be given the exclusive right to consent to the adoption of a child born out of wedlock. Because most adoptions involve newborn infants or very young children,7 it is appropriate at the outset to focus on the significance of the difference in such cases.

Both parents are equally responsible for the conception of the child out of wedlock.8 But from that point on through pregnancy and infancy, the differences between the male and the female have an important impact on the child’s destiny. Only the mother carries the child; it is she who has the constitutional right to decide whether to bear it or not.9 In many *405eases, only the mother knows who sired the child, and it will often be within her power to withhold that fact, and even the fact of her pregnancy, from that person. If during pregnancy the mother should marry a different partner, the child will be legitimate when born, and the natural father may never even know that his “rights” have been affected. On the other hand, only if the natural mother agrees to marry the natural father during that period can the latter’s actions have a positive impact on the status of the child; if he instead should marry a different partner during that time, the only effect on the child is negative, for the likelihood of legitimacy will be lessened.

These differences continue at birth and immediately thereafter. During that period, the mother and child are together;10 the mother’s identity is known with certainty. The father, on the other hand, may or may not be present; his identity may be unknown to the world and may even be uncertain to the mother.11 These natural differences between unmarried fathers and mothers make it probable that the mother, and not the father or both parents, will have custody of the newborn infant.12

*406In short, it is virtually inevitable that from conception through infancy the mother will constantly be faced with decisions about how best to care for the child, whereas it is much less certain that the father will be confronted with comparable problems. There no doubt are cases in which the relationship of the parties at birth makes it appropriate for the State to give the father a voice of some sort in the adoption decision.13 But as a matter of equal protection analysis, *407it is perfectly obvious that at the time and immediately after a child is born out of wedlock, differences between men and women justify some differential treatment of the mother and father in the adoption process.

Most particularly, these differences justify a rule that gives the mother of the newborn infant the exclusive right to consent to its adoption. Such a rule gives the mother, in whose sole charge the infant is often placed anyway, the maximum flexibility in deciding how best to care for the child. It also gives the loving father an incentive to marry the mother,14 and has no adverse impact on the disinterested father. Finally, it facilitates the interests of the adoptive parents, the child, and the public at large by streamlining the often traumatic adoption process and allowing the prompt, complete, and reliable integration of the child into a satisfac*408tory new home at as young an age as is feasible.15 Put most simply, it permits the maximum participation of interested natural parents without so burdening the adoption process that its attractiveness to potential adoptive parents is destroyed.

This conclusion is borne out by considering the alternative rule proposed by appellant. If the State were to require the consent of both parents, or some kind of hearing to explain why either’s consent is unnecessary or unobtainable,16 it would unquestionably complicate and delay the adoption process. Most importantly, such a rule would remove the mother’s freedom of choice in her own and the child’s behalf without also relieving her of the unshakable responsibility for the care of the child. Furthermore, questions relating to the adequacy of notice to absent fathers could invade the mother’s privacy,17 cause the adopting parents to doubt the reliability *409of the new relationship, and add to the expense and time required to conclude what is now usually a simple and certain process.18 While it might not be irrational for a State to conclude that these costs should be incurred to protect the interest of natural fathers, it is nevertheless plain that those costs, which are largely the result of differences between the mother and the father, establish an imposing justification for some differential treatment of the two sexes in this type of situation.

With this much the Court does not disagree; it confines its holding to cases such as the one at hand involving the adoption of an older child against the wishes of a natural father who previously has participated in the rearing of the child and who admits paternity. Ante, at 392-393. The Court does conclude, however, that the gender basis for the classification drawn by § 111 (1) (c) makes differential treatment so suspect that the State has the burden of showing not only that the rule is generally justified but also that the justification holds equally true for all persons disadvantaged by the rule. In its view, since the justification is not as strong for some indeterminately small part of the disadvantaged class as it is for the class as a whole, see ante, at 393, the rule is invalid under the Equal Protection Clause insofar as it applies to that subclass. With this conclusion I disagree.

If we assume, as we surely must, that characteristics possessed by all members of one class and by no members of the other class justify some disparate treatment of mothers and fathers of children born out of wedlock, the mere fact that the statute draws a “gender-based distinction,” see ante, at 389, *410should not, in my opinion, give rise to any presumption that the impartiality principle embodied in the Equal Protection Clause has been violated.19 Indeed, if we make the further undisputed assumption that the discrimination is justified in those cases in which the rule has its most frequent application — cases involving newborn infants and very young children in the custody of their natural mothers, see nn. 7 and 12, supra — we should presume that the law is entirely valid and require the challenger to demonstrate that its unjust applications are sufficiently numerous and serious to render it invalid.

In this case, appellant made no such showing; his demonstration of unfairness, assuming he has made one, extends only to himself and by implication to the unknown number of fathers just like him. Further, while appellant did nothing to inform the New York courts about the size of his subclass and the overall degree of its disadvantage under § 111 (l)(c), the New York Court of Appeals has previously concluded that the subclass is small and its disadvantage insignificant by comparison to the benefits of the rule as it now stands.20

*411The mere fact that an otherwise valid general classification appears arbitrary in an isolated case is not a sufficient reason *412for invalidating the entire rule.21 Nor, indeed, is it a sufficient reason for concluding that the application of a valid rule in a hard case constitutes a violation of equal protection principles.22 We cannot test the conformance of rules to the principle of equality simply by reference to exceptional cases.

Moreover, I am not at all sure that § 111 (1) (c) is arbitrary even if viewed solely in the light of the exceptional circumstances presently before the Court. This case involves a dispute between natural parents over which of the two may adopt the children. If both are given a veto, as the Court requires, neither may adopt and the children will remain illegitimate. If, instead of a gender-based distinction, the veto were given to the parent having custody of the child, the mother would prevail just as she did in the state court.23 *413Whether or not it is wise to devise a special rule to protect the natural father who (a) has a substantial relationship with his child, and (b) wants to veto an adoption that a court has found to be in the best interests of the child, the record in this case does not demonstrate that the Equal Protection Clause requires such a rule.

I have no way of knowing how often disputes between natural parents over adoption of their children arise after the father “has established a substantial relationship with the child and [is willing to admit] his paternity,” ante, at 393, but has previously been unwilling to take steps to legitimate his relationship. I am inclined to believe that such cases are relatively rare. But whether or not this assumption is valid, the far surer assumption is that in the more common adoption situations, the mother will be the more, and often the only, responsible parent, and that a paternal consent requirement will constitute a hindrance to the adoption process. Because this general rule is amply justified in its normal application, I would therefore require the party challenging its constitutionality to make some demonstration of unfairness in a significant number of situations before concluding that it violates *414the Equal Protection Clause. That the Court has found a violation without requiring such a showing can only be attributed to its own “stereotyped reaction” to what is unquestionably, but in this case justifiably, a gender-based distinction.

II

Although the substantive due process issue is more troublesome,24 I can briefly state the reason why I reject it.

I assume that, if and when one develops,25 the relationship between a father and his natural child is entitled to protection against arbitrary state action as a matter of due process. See Stanley v. Illinois, 405 U. S. 645, 651.26 Although the Court has not decided whether the Due Process Clause provides any greater substantive protection for this relationship than simply against official caprice,27 it has indicated that an adoption decree that terminates the relationship is constitutionally justified by a finding that the father has abandoned or mistreated the child. See id., at 652. In my view, such a decree may also be justified by a finding that the adoption will serve *415the best interests of the child, at least in a situation such as this in which the natural family unit has already been destroyed, the father has previously taken no steps to legitimate the child, and a further requirement such as a showing of unfitness would entirely deprive the child — and the State— of the benefits of adoption and legitimation.28 As a matter of legislative policy, it can be argued that the latter reason standing alone is insufficient to sever the bonds that have developed between father and child. But that reason surely avoids the conclusion that the order is arbitrary, and is also sufficient to overcome any further protection of those bonds that may exist in the recesses of the Due Process Clause. Although the constitutional principle at least requires a legitimate and relevant reason and, in these circumstances, perhaps even a substantial reason, it does not require the reason to be one that a judge would accept if he were a legislator.

Ill

There is often the risk that the arguments one advances in dissent may give rise to a broader reading of the Court’s opinion than is appropriate. That risk is especially grave when the Court is embarking on a new course that threatens to interfere with social arrangements that have come into use over long periods of time. Because I consider the course on which the Court is currently embarked to be potentially most serious, I shall explain why I regard its holding in this case as quite narrow.

The adoption decrees that have been entered without the consent of the natural father must number in the millions. An untold number of family and financial decisions have been made in reliance on the validity of those decrees. Because *416the Court has crossed a new constitutional frontier with today’s decision, those reliance interests unquestionably foreclose retroactive application of this ruling. See Chevron Oil Co. v. Huson, 404 U. S. 97, 106-107. Families that include adopted children need have no concern about the probable impact of this case on their familial security.

Nor is there any reason why the decision should affect the processing of most future adoptions. The fact that an unusual application of a state statute has been held unconstitutional on equal protection grounds does not necessarily eliminate the entire statute as a basis for future legitimate state action. The procedure to be followed in cases involving infants who are in the custody of their mothers — whether solely or jointly with the father — or of agencies with authority to consent to adoption, is entirely unaffected by the Court’s holding or by its reasoning. In fact, as I read the Court’s opinion, the statutes now in effect may be enforced as usual unless “the adoption of an older child is sought,” ante, at 392, and “the father has established a substantial relationship with the child and [is willing to admit] his paternity.” Ante, at 393. State legislatures will no doubt promptly revise their adoption laws to comply with the rule of this case, but as long as state courts are prepared to construe their existing statutes to contain a requirement of paternal consent “in cases such as this,” ibid., I see no reason why they may not continue to enter valid adoption decrees in the countless routine cases that will arise before the statutes can be amended.29

In short, this is an exceptional case that should have no effect on the typical adoption proceeding. Indeed, I suspect *417that it will affect only a tiny fraction of the cases covered by the statutes that must now be rewritten. Accordingly, although my disagreement with the Court is as profound as that fraction is small, I am confident that the wisdom of judges will forestall any widespread harm.

I respectfully dissent.