Background: The objectives were to estimate the size of homeless family population in Paris region, to describe their living conditions and health and to analyse the impact of homelessness on children’s growth and development, which was never investigated in France. Methods: A cross-sectional survey was conducted on a random sample of homeless sheltered families in 2013. Families were interviewed in 17 languages and a nurse took anthropometric measures, blood samples and collected health data from child health reports. Results: The population size was estimated at 10 280 families. Half were single-parent female families and 94% were born outside France. Most families had experienced housing instability and 94% were living below the poverty line (828 euros/month). Malnutrition was a major problem: the prevalence of food insecurity was high (77% of parents and 69% of children), as well as anaemia (50% of mothers and 38% of children), overweight (38% of mothers and 22% of children) and obesity (32% of mothers and 4% of children). High rates of depressive disorders were found in 30% of homeless mothers and 20% of children had signs of possible mental health disorders. Discussion: These first results highlight the important number of families among the homeless population in Paris region. Families differed from other homeless people regarding social characteristics such as birthplace, single-parent status and residential instability that are likely to influence schooling, social ties, health and access to care. These results demonstrate the need for urgent actions targeting homeless families, in terms of reducing housing instability and providing adequate care, especially for children.