This study aimed to establish a profile of users of the mental health service for homeless in Cork, comparing this group with those attending a General Adult Service. The homeless group were significantly more likely to be male (89% v 46%), unemployed (96% v 68%), unmarried (98% v 75%) and under 65 (94% v 83%). Diagnostically, there was a significantly higher prevalence of schizophrenia (50% v 34%); personality disorder (37% v 11%) and substance dependence (74% v 19%) in the homeless service users. They were more likely to have a history of deliberate self harm (54% v 21%) and violence (48% v 10%). Severe mental illness has a high prevalence in the homeless population, with particularly high levels of factors associated with suicide and homicide. Poor compliance and complexity of illness lead to a requirement for significant input from multidisciplinary mental health teams members.