Background: Specific problems in sampling methodology, case-finding strategies and a standardised needs assessment in mentally ill homeless people have contributed to their being neglected as a mental health care clientele. Method: We assessed a representative sample of homeless people “n=102” in the highly industrialised city of Mannheim “Germany” regarding their prevalence of mental disorders “using the SCID” and their needs for mental health care “using the NCA”. Results: We found high prevalences, with 68.6% of all assessed homeless persons having a current mental disorder. Thus, needs for mental health care were very common, with unmet needs predominating in all problem areas, which was supported by a very weak service utilization. Thus, even in a region with a comprehensive community mental health care network, like the study area, mentally ill homeless people are widely under-provided. Conclusions: Results suggest that the traditional shelter system for homeless people carries most of the mental health care burden for their clientele and must be supported by adequate interventions from community-based mental health care services. A closer connection of both sectors and a better co-ordination of the care offers seems to be a prerequisite for helping to reduce unmet mental health care needs in this specific high-risk group.