This study of a frequently endorsed, but untested, model of outpatient treatment for persons with coexisting severe mental illness and substance use disorders assessed how the amount of treatment services delivered was related to an individual's global severity of illness, whether different modes of treatment were related to different aspects of illness, how noncompliance with treatment was related to the severity of illness and amount of services delivered, and how the diagnosis of schizophrenia/schizoaffective influenced these issues. Participants with high total severity of illness (TSI) received about twice the number of appointments (20.7 vs. 12.3) per month as those with low TSI scores. Higher TSI was also related to a DSM-IV diagnosis of schizophrenia/schizoaffective, being in a lower "phase" of treatment, representative payee benefit management, homelessness, and more hospitalizations. Participants with higher psychiatric symptom severity received significantly more case management and medication services, but not group therapy or day treatment. Severity of substance use condition was significantly related only to case management. This model of treatment was found to be successful in delivering higher levels of treatment services to those needing them.