Background Knowledge about the health impacts of the absence of health insurance for migrants with precarious status (MPS) in Canada is scarce. MPS refer to immigrants with authorized but temporary legal status (i.e. temporary foreign workers, visitors, international students) and/ or unauthorized status (out of legal status, i.e. undocumented). This is the first large empirical study that examines the social determinants of self-perceived health of MPS who are uninsured and residing in Montreal. Methods and findings Between June 2016 and September 2017, we performed a cross-sectional survey of uninsured migrants in Montreal, Quebec. Migrants without health insurance (18+) were sampled through venue-based recruitment, snowball strategy and media announcements. A questionnaire focusing on sociodemographic, socioeconomic and psychosocial characteristics, social determinants, health needs and access to health care, and health self-perception was administered to 806 individuals: 54.1% were recruited in urban spaces and 45.9% in a health clinic. 53.9% were categorized as having temporary legal status in Canada and 46% were without authorized status. Regions of birth were: Asia (5.2%), Caribbean (13.8%), Europe (7.3%), Latin America (35.8%), Middle East (21%), Sub-Saharan Africa (15.8%) and the United States (1.1%). The median age was 37 years (range:18-87). The proportion of respondents reporting negative (bad/fair) self-perception of health was 44.8%: 36.1% among migrants with authorized legal status and 54.4% among those with unauthorized status (statistically significant difference; p<0.001). Factors associated with negative self-perceived health were assessed using logistic regression. Those who were more likely to PLOS ONE |