Following a jury trial, appellant was convicted of unlawful possession of heroin with intent to distribute, in violation of D.C.Code § 48-904.01(a)(l) (2001), and sentenced to 144 months (twelve years) in prison followed by five years of supervised release. On direct appeal, this court affirmed his conviction by unpublished Memorandum Opinion and Judgment on April 21, 2005. Appellant subsequently filed a motion to reduce sentence pursuant to Super. Ct.Crim. R. 35, which the trial court denied. On appeal, he argues that the trial court abused its discretion in denying his motion and, for the first time on appeal, contends that his sentence violated the Eighth Amendment in that it was disproportionate to the crime committed. We affirm.

We review the denial of a motion for the reduction in sentence for an abuse of discretion. See Walden v. United States, 366 A.2d 1075, 1076-77 (D.C. 1976). In so doing, “[t]his court has long refused, in considering ... an appeal of a post-trial decision on sentence reduction, to review ... sentences which are within statutory limits, on the ground that such sentences are too severe.” Crawford v. United States, 628 A.2d, 1002, 1003-1004 (D.C. 1993) (citations and internal quotation marks omitted). Indeed, “[gjenerally, sentences within statutory limits are unre-viewable aside from constitutional considerations.” Id. at 1003-1004 (citation and internal quotation marks omitted).

Here, appellant’s sentence fell well within the thirty-year statutory maximum for the offense of which he was convicted. D.C.Code § 48-904.01(a)(2)(A) (2001). In his motion to reduce sentence appellant’s primary argument was that “[h]ad Mr. Cook received a ‘guideline sentence’ under the current sentencing guidelines for the same offense, his sentence would have been significantly less than his current sentence.” However, the Superior Court Voluntary Sentencing Guidelines were not in effect at the time of sentencing and, regardless, being voluntary would not have compelled the trial court to impose a lesser sentence. Given our “very limited” standard of review on these issues, we are not persuaded that the trial court abused its discretion in denying the motion. See Walden, supra, 366 A.2d at 1077.

Turning to appellant’s constitutional argument, we note that “[w]here a defendant has failed to raise an available challenge to his conviction on direct appeal, he may not raise that issue on collateral attack unless he shows both cause for his failure to do so and prejudice as a result of his failure.”1 See Head v. United *508States, 489 A.2d 450, 451 (D.C. 1985) (citations omitted). Here, appellant failed to raise his Eighth Amendment claim on direct appeal, instead raising it for the first time as part of this appeal. In so doing he proffers no cause for this failure. Thus, we “need not decide whether he suffered prejudice or even if the trial court was in error.” See id. at 451 n. 5 (citation omitted). Accordingly, because appellant has failed to demonstrate the requisite cause for his failure to have raised the issue on direct appeal, “his contention here is foreclosed.” See id. at 451.

Even if we were to consider appellant’s claim on the merits, we are not convinced that appellant’s sentence was so disproportionate as to contravene the Cruel and Unusual Punishment Clause of the Eighth Amendment.2 We are mindful that following the Supreme Court’s decisions in Harmelin v. Michigan, 501 U.S. 957, 111 S.Ct. 2680, 115 L.Ed.2d 836 (1991), and Ewing v. California, 538 U.S. 11, 123 S.Ct. 1179, 155 L.Ed.2d 108 (2003), the standard for claims of disproportionate sentences has been narrowed3 and, at a minimum, now appears to require a showing that a sentence is “grossly disproportionate” to the crime. See Crawford, supra, 628 A.2d at 1003; Moore, supra, note 2, 608 A.2d at 145 n. 3. Under this standard, we are not convinced that appellant’s sentence was “grossly disproportionate” to the crime. It was well within the statutory maximum and, as the government notes in its brief, there were a number of aggravating circumstances affecting the length of sentence imposed by the trial court. See Hutto v. Davis, 454 U.S. 370, 102 S.Ct. 703, 70 L.Ed.2d 556 (1982) (upholding a sentence of forty years imprisonment for possession with intent to distribute nine ounces of marijuana). Accordingly, the judgment on appeal herein is hereby affirmed.

So ordered.

concurring:

With a measure of reluctance, I concur in the judgment affirming the denial of Cook’s motion to reduce his sentence. Even assuming arguendo, that his Eighth Amendment claim has not been waived1— *509and my colleagues in the majority hold that it has been — I, like the court, do not believe, in the light of recent Supreme Court precedent, that Cook’s sentence, which imposed imprisonment for only forty percent of the statutory thirty-year maximum, was “so disproportionate as to contravene the Cruel and Unusual Punishment Clause.” See Harmelin v. Michigan, 501 U.S. 957, 1001, 111 S.Ct. 2680, 115 L.Ed.2d 836 (1991) (plurality opinion); Ewing v. California, 538 U.S. 11, 20, 123 S.Ct. 1179, 155 L.Ed.2d 108 (2003) (plurality opinion); Hutto v. Davis, 454 U.S. 370, 370-75, 102 S.Ct. 703, 70 L.Ed.2d 556 (1982) (per curiam).2 Moreover, in the absence of an error of law or of some extraordinary circumstance not here present, we, as an appellate court, lack the authority to review a sentence that is within statutory limits. In re L.J., 546 A.2d 429, 434-36 (D.C. 1988); Walden v. United States, 366 A.2d 1075, 1076-77 (D.C. 1976).

Nevertheless, in my judgment the sentence in this case is so severe that it warrants brief comment, albeit obiter dictum, at the appellate level. Cook contends, without contradiction by the government, that the twelve-year term of imprisonment imposed by the judge for unarmed possession of heroin -with intent to distribute it (PWID) was:

1. approximately four times as long as a sentence which would probably have been imposed pursuant to the Superior Court’s “Voluntary Sentencing Guidelines” (SCVSG);

2. substantially greater than the guideline range for PWID while aimed;

3. in excess of the range for several aimed and violent offenses, including, inter alia, armed robbery and possession of a firearm during a crime of violence; and

4. approximately three times as harsh as the penalty range under the federal sentencing guidelines.

The SCVSG were issued on June 14, 2004, ten months after Cook was sentenced, but they had been in effect for approximately sixteen months when the judge denied Cook’s motion to reduce sentence. Obviously, the guidelines did not apply to Cook’s case when he was sentenced, for they were not yet in existence at the time. Moreover, they are voluntary guidelines, and the judge was not obliged to follow them when he acted on Cook’s Rule 35 motion or, indeed, at any time. Nevertheless, the guidelines are revealing, for they were “based on historical data *510from the Superior Court Criminal Information System Computer over the past eight years,3 with some adjustments for consistency and symmetry.” SCVSG at 1-1. In other words, the guidelines provide a sentencing judge with information regarding the range of sentence typically imposed by his or her colleagues under comparable circumstances over a substantial period of time.

At the time the trial judge denied Cook’s motion to reduce sentence, he had access to information tending to show that the sentence he had imposed — imprisonment for 144 months, i.e., for twelve years — was roughly four times as harsh as the typical punishment for an offender who had committed a similar crime and who had a similar prior criminal record. In my opinion, the imposition of such a sentence, and the refusal to reconsider it, were not only unfair to the defendant and his family4 (who will be forced to look on as other inmates who have committed similar or worse crimes are released from prison, while Cook has a great many more years to serve), but they also present to the general public an image of judicial arbitrariness, inconsistency, and unfairness, to the detriment of the reputation of the court and of the judicial system. It is worth noting that Cook has already served almost four years, with eight more years to go.

“Our duty, to paraphrase Mr. Justice Holmes in a conversation with Judge Learned Hand, is not to do justice, but to apply the law and hope that justice is done.” Bifulco v. United States, 447 U.S. 381, 402, 100 S.Ct. 2247, 65 L.Ed.2d 205 (1980) (Burger, C.J., concurring). I am not persuaded that justice has been done in this case.5 Having sworn to uphold the law, however, I am constrained to join my colleagues in affirming the judgment. Cf. Moore v. United States, 608 A.2d 144, 146-48 (D.C. 1992) (concurring opinion).