This study investigated the accuracy of various indices involving the MMPI-A scales, ACK, MAC-R, and PRO in diagnosing substance abuse in a sample of 79 psychiatric inpatients. In the full sample, 89.9% of the cases were accurately classified by at least one of the three scales. The overall accuracy of classification was similar among males, females, Caucasians, and African Americans, although there was a tendency for more false positive misclassifications among males. Profile code type moderated the accuracy of classification with greatest accuracy for code types including Scales 1, 2, 3, 5, or 0 and least accuracy for code types including Scales 4, 6, or 9. ACK, MAC-R, and PRO were better at screening out cases of substance abuse than in accurately identifying those adolescents who were using substances.