At this time in our nation when the prevalence of substance abuse has swollen to alarming levels and when large numbers of seriously mentally ill persons live in the community as a result of deinstitutionalization, persons with both substance abuse and mental illness test the skills and limits of service agencies. The clinical characteristics, social conditions, functional deficits, and treatment and service needs of these dually diagnosed patients must be better understood in order to develop services which adequately address both their psychiatric and substance abuse problems. In this five-year project, the clinical characteristics, substance use and abuse patterns, functional status, quality of life and treatment histories of over 400 seriously mentally ill patients admitted to a large inner-city community mental health center will be studied. The principal objectives are the assessment of the prevalence and patterns of substance abuse in this population and the evaluation of the relationship of substance abuse to illness course during a one-year follow-up period. Patients with substance abuse will be compared to those who are not dually diagnosed at baseline with regard to demographics, DSM-III diagnoses, functional status, quality of life, and length of index hospitalization. One-year follow-up evaluations will assess the stability of DSM-III diagnoses and substance abuse patterns over time and examine the impact of substance abuse on compliance with aftercare, interim use of treatment services, total time spent in the hospital during the follow-up year, as well as severity of psychiatric symptomatology and substance abuse, functional status, and quality of life at the one year follow-up. These data will guide the subsequent development of experimental treatment research on substance abuse in the seriously mentally ill and assist urban mental health centers in establishing priorities for treatment of substance abuse among various subgroups of these patients.