OBJECTIVES: To validate the prototype Adolescent Treatment Outcomes Module (ATOM), examine its sensitivity to clinical change, and determine its feasibility for administration in routine clinical settings. METHOD: A sample of 67 adolescents, aged 11 through 18, was selected from new patients at two inpatient and two outpatient mental health programs. Adolescents and parents completed the ATOM and validating instruments at intake, 1 week postintake, and again at 6 months. RESULTS: Nine self-report symptoms predicted positive diagnoses of oppositional defiant, conduct, anxiety, and depressive disorders on the basis of structured diagnoses, with sensitivities of 0.7 to 0.8. Test-retest correlations for outcome scales were largely excellent (>0.70). Scales that measured functioning at home, in school, and in the community were moderately correlated in the expected direction with global functioning. Decreases in symptom severity and functional impairment were generally associated with decreases in validating instruments. Administration time averaged 25 minutes for adolescents and 28 minutes for parents. CONCLUSIONS: Both parents and adolescents readily completed the ATOM. Module scales demonstrated excellent reliability and good to fair concurrent validity. The ATOM was able to detect change and its absence.