Laura Henderson, through counsel, appeals the magistrate judge’s decision 1 affirming the Social Security Commissioner’s denial of her application for social security income. Henderson asserts the Administrative Law Judge (ALJ) erred by (1) concluding her post-traumatic stress disorder (PTSD) was not a severe mental impairment, and (2) failing to develop a full and fair record. We address each issue in turn, and affirm. 2

I.

Henderson contends the ALJ erred by not finding her PTSD to be a severe mental impairment. We decline to address this argument on appeal because Henderson failed to raise it before the district court, instead asserting the ALJ erred by not finding her depression — a distinct mental illness — to be a severe impairment. See Crawford v. Comm’r of Soc. Sec., 363 F.3d 1155, 1161 (11th Cir. 2004); Jones v. Apfel, 190 F.3d 1224, 1228 (11th Cir. 1999).

II.

Henderson argues the ALJ failed to develop a full and fair record. Specifical *305 ly, she asserts the ALJ’s failure to request and obtain an updated mental residual functional capacity (RFC) assessment from Dr. Andres Nazario constitutes reversible error.

“Because a hearing before an ALJ is not an adversary proceeding, the ALJ has a basic obligation to develop a full and fair record.” Cowart v. Schweiker, 662 F.2d 731, 735 (11th Cir. 1981). “Nevertheless, there must be a showing of prejudice before we will ... remand[ ] to the [Commissioner] for further development of the record.” Brown v. Shalala, 44 F.3d 931, 935 (11th Cir. 1995).

In this case, Henderson does not explain how the absence of a mental RFC assessment from the record precluded the ALJ from making an informed disability determination. Nor does she explain how such an assessment would have affected the ALJ’s overall disability determination. Because Henderson has not shown the requisite prejudice, we affirm.

AFFIRMED.