Patients were 87 adolescents (both genders) in treatment for conduct and substance abuse problems. Most controls (n=85; both genders) came from patients' neighborhoods. Assessments included the Diagnostic Interview Schedule for Children, Composite International Diagnostic Instrument-Substance Abuse Module, Child Behavior Checklist, and others. Patients' data guided clinical care. Findings show that youths' self-reports significantly discriminated patients from controls in DSM-IV conduct and substance use disorders (CD, SUD) and in numerous associated measures. CD and SUD symptoms correlated strongly; however, some patients apparently minimized symptoms. Youths' self-reports did not discriminate patients from controls in attention-deficit/hyperactivity disorder (ADHD) or major depression (MDD). Parent information raised prevalence rates of ADHD and MDD, which then discriminated patients from controls; however, patients and parents usually disagreed on MDD and ADHD diagnoses. The study concluded that despite some dissimulation, patients' self-reports of CD and SUD correlated highly and had superb discriminative validity, making them useful for treatment and research. Self-reports of ADHD and MDD, apparently lacking discriminative validity, were less useful. Parent reports improve these discriminations but present additional problems. 4 tables, 1 figure, and 43 references