Across the country there are data suggesting that, among the mentally ill, homelessness is associated with increased criminal behavior. The research literature to date suggests that neither mental disorder nor homelessness alone adequately accounts for an increase in risk for violent crime. Studies, however, linking the homeless mentally ill with violent crime raise the possibility that homelessness and mental disorder interact in some volatile way. What might explain this relationship? It is possible that factors associated with homelessness may place the mentally ill at increased risk for violent criminal behavior. Alternatively, the homeless mentally ill may simply receive differential treatment by the criminal justice and forensic mental health systems. Criminological theory suggests that it is not increased risk of dangerous behavior, but an increased vulnerability to arrest that accounts for these patterns. Using a case-control design, this study seeks to explore this issue systematically. Two sub-studies are planned. The first project examines "risk" by exploring the contribution of homelessness to violent criminal behavior in the mentally ill. Data from 150 homeless and 150 domiciled mentally disordered offenders will be examined. The second project explores "criminalization" by discriminating between two groups of homeless mentally ill persons: 150 who have a history of criminal behavior and 150 matched control persons who do not. The data will be derived from court records, hospital records, patient and family interviews, and standard diagnostic instruments. This study promises to add substantially to our knowledge of the role of homelessness in mediating the link between mental illness and violent criminal behavior. It will not only break new ground but also lay the foundation for future prospective studies of the causes of violence in society.