OBJECTIVE: The study compared patterns of previous mental health service use among 100 homeless men with schizophrenia and 100 men with schizophrenia who had never been homeless and explored whether differences in use of services were related to severity of illness. METHODS: Subjects were recruited from shelters, clinics, and inpatient psychiatric programs in New York City. Clinical interviewers used standardized research instruments to collect data on psychiatric treatment history, mental health service use within the past 12 months, adequacy of discharge planning from the most recent psychiatric hospitalization, positive and negative-symptom levels, and presence of concurrent substance abuse and antisocial personality disorder. RESULTS AND CONCLUSIONS: Homeless subjects and never-homeless subjects had similar treatment histories and recent patterns of inpatient, outpatient, and emergency service use. However, the homeless men were more likely to have been discharged from their most recent psychiatric hospitalization against medical advice and to have less adequate discharge planning for living arrangements, aftercare, and finances. Inadequacies in discharge planning were most apparent among homeless men with triple disorders of schizophrenia, substance abuse, and antisocial personality disorder.