BACKGROUND: Mayotte Island, located in the Indian Ocean, is a French overseas departmental community with certain specificities: recent development of sanitary institutions, significant immigration, free access to care for legal residents but with co-payments for irregular residents, the absence of many of the social benefits which exist in mainland France and poor or non-existent health information systems. We report here the first population-based survey describing the links between health, migration and healthcare utilization in this territory. METHODS: Cross sectional population-based study using a three-stage random sample (geographic areas, households, individuals). In all, 2105 individuals were interviewed either in French, Shimaore or Kibushi (response rate=96%), using a questionnaire adapted to the context of Mayotte Island after a preliminary qualitative survey. Descriptive analyses and logistic regression models were performed. RESULTS: Foreigners make up 40% of the Mayotte population (total 186,452 inhabitants), of which one-quarter are children born in Mayotte and 80% have no regular residence status. The median length of residence of migrant foreigners is 10 years. Foreigners represent a majority of the female population, of the 20 to 35 years old population and of the urban areas. Main determinants for migration were economical (50%) or family-related (26%). Health was stated as a cause of migration by 11% of migrants. The social situation of foreigners is more precarious and their perceived health poorer than those of the French. Their access to care is also perceived as more difficult. We did not observe any notable difference in terms of frequency of healthcare attendance over the last 12 months between the two groups, but foreigners have consulted less often private GPs and more often traditional practitioners than French. CONCLUSION: In this overseas French island, the migrant population is numerous and resident for a long time. Their main motivations to immigrate are economic and family-related. They report hurdles to healthcare related with their precarious living conditions, including their illegal residence status.