CONTEXT: Marseille, the second largest city in France, has a large population of homeless persons. A mental health outreach team was created in 2005 as a response to high rates of mental illness among this group. In a national political context where security is a government priority, a new central police station was created in Marseille in 2006 to address robberies, violence and illegal traffic in the downtown area of the city. While not directly related to such crimes, police also are responsible for public safety or behavioral issues related to the presence of individuals who are homeless in this area. OBJECTIVE: This report on a two-year pilot study (2009-2011) addresses collaborative work between a mental health outreach team and the police department responding to the clinical needs of persons who are homeless with serious psychiatric disorders. It also describes the homeless persons' interactions with, and perceptions of the presence of, police and mental health professionals on the streets. METHODS: Investigators adopted a mixed-methods approach. Data were collected on 40 interactions using brief standardized report for each interaction. Focus groups were conducted with police officers, outreach team members, peer workers, and service users. Minutes of partnership meetings between police officers and outreach workers also served as a source of qualitative data. RESULTS: Outreach workers initiated just over half (n=21) of the encounters (n=40) between police and outreach workers. Interactions mainly involved persons with psychosis (77%), the vast majority (80%) of which involved persons in an acute phase of psychosis. Two key themes that emerged from data analysis included the violent nature of life on the streets and the high percentage of ethnic minorities among subjects of the interactions. In addition, it was found that the practices of the outreach workers are sometimes similar to those of the police, especially when outreach workers use coercive methods. "Users" (homeless persons) described police as sometimes using less coercion than the outreach team, and noted that they were more fearful of psychiatrists than police. CONCLUSION: Formal initiatives between mental health outreach teams and police departments involve some common street practices. This study demonstrates the potential for closer working relationships between the two parties to help persons who are homeless with mental illnesses receive needed care, and to reduce inappropriate coercion including involuntary hospitalization and arrests.