OBJECTIVE: The aim of this report was to examine the accuracy of diagnosing substance use disorders in manic adolescents with bipolar disorder. METHODS: The substance use disorder modules of the KSADS-PL were administered to a sample of 80 manic adolescents (12-21 years old) with co-occurring bipolar and substance use disorders. Initial substance use disorder diagnoses obtained from the KSADS-PL were then compared to a best-estimate diagnosis derived from all available information, including a second diagnostic interview, the Child Semi-Structured Assessment for the Genetics of Alcoholism, Adolescent version (C-SSAGA-A). RESULTS: Relatively low diagnostic agreement was achieved across the initial and the best estimate diagnoses for both alcohol and cannabis use disorders. Age, race, and sex did not predict diagnostic agreement between the two evaluations. CONCLUSIONS: Results of this study call for more research on diagnosing substance use disorders and suggest that a single interview alone may not be accurate for diagnosing substance use disorders in manic adolescents with bipolar disorder.