The healthcare utilization of homeless people is generally considered insufficient, and studies often suffer from methodological bias (institutionalized vs. street samples). To adapt public health policies in France, epidemiological data on this population are scarce. The objective of this study was to analyze the use of psychiatric care by homeless people with mental health problems in the Greater Paris area and to define the factors influencing this use. The data were from the SAMENTA survey performed in 2009 with a representative random street sample of 859 homeless people from the Greater Paris area. The survey studied the use of psychiatric care (lifelong use, current follow-up, discontinuation of follow-up and treatment) and factors potentially associated with this use for people with a diagnosis of a psychotic, mood or anxiety disorder, with the diagnosis established with an original survey device. Because of our complex sampling design, we describe data for only a weighted estimated prevalence, weighted estimation of the number of people in the population (N) and unweighted total subgroup studied in the survey (n). Among 840 homeless people with useable data, 377 (N = 9762) had a psychiatric disorder. The use of whole-life care for these people may seem high, estimated at 68.7%, but few people were followed up for their disorders (18.2%); individuals with a psychotic disorder were more frequently followed up (36.5%) than others were (p < 0.05). Among those followed up (n = 86, N = 1760), 63.0% were taking medication. Access to care for these people seemed preserved, but the maintenance of care seemed problematic; indeed, among people with a lifelong whole use of care (n= 232, N = 6705), 72.3% could be considered to have discontinued care. The factors that improved lifetime health service utilization or follow-up were socio-demographic (age < 42 years, more educated), social (with social security coverage, not living in a hotel), and medical (psychotic disorder, personality disorder, suicide risk, somatic chronic illness, perception of mental suffering). Improving the care of homeless people with psychiatric disorders requires improving access to care for those isolated from the health system (in particular those living in hotels) and to guarantee continuity of care, by adapting the organization of the care system and promoting social rehabilitation.