Selected mental health and social characteristics of 51 homeless persons drawn as a probability sample from missions are compared to those of 1,338 men aged 18-64 years living in households from the NIMH Epidemiologic Catchment Area survey conducted in Eastern Baltimore. Differences between the two groups were small with respect to age, race, education, and military service but the differences in mental health status, utilization patterns, and social dysfunction were large. About one-third of the homeless scored high on the General Health Questionnaire which measures distress. A similar proportion had a current psychiatric disorder as ascertained by the Diagnostic Interview Schedule (DIS), with the homeless exhibiting higher prevalence rates in every DIS/DSM III diagnostic category compared to domiciled men. Homeless persons reported higher rates of hospitalization than household men for both mental (33 per cent vs 5 per cent) and physical (20 per cent vs 10 per cent) problems but a lower proportion received ambulatory care (41 per cent vs 50 per cent). Social dysfunction among the homeless was indicated by fewer social contacts and higher rates of arrests as adults than domiciled men (58 per cent vs 24 per cent), including multiple arrests (38 per cent vs 9 per cent) and felony convictions (16 per cent vs 5 per cent). Implications of these findings are discussed in terms of research and health policy.