The frequency, severity, recognition, cost, and outcomes of adolescent substance use comorbidity were analyzed in the Fort Bragg Demonstration Project. Comorbidity was defined as the co-occurrence of substance use disorder (SUD) with other psychiatric diagnosis. The sample consisted of 428 adolescent clients whose providers' diagnoses were compared with research diagnoses. The project identified 59 clients (13.8%) with SUD, all with additional psychiatric diagnoses. Providers recognized only 21 of these 59 comorbid cases. The frequency and severity of comorbidity did not differ between service system samples, although recognition did. Comorbid clients had more behavior problems and more functioning impairment, and their average treatment cost ($29,057) was more than twice as high as that of noncomorbid clients ($13,067). Mental health outcomes were not influenced by type of service system, comorbid diagnosis, or treatment. Screening for and prevention of SUD are discussed as a potential cost-savings opportunity in mental health services.