The homeless population is difficult to define and its number difficult to evaluate. In France, it is estimated that almost 4 million people living in substandard accommodation, and 85 000 homeless people. Most homeless people rarely frequent public spaces. One-third have a job, one-quarter live with children, and one-third are between 18 and 29 years old. Shared characteristics include a collapse of social ties and a complete lack of stable accommodation. There are no illnesses specific to homeless people, but their epidemiology differs from the general population: the incidence rate of tuberculosis is 30 times higher; for example. Medical care often arrives far too late. As a result, functional deficits are common, often following serious accidents, and hospitalization is three times more frequent. A chronic disease is present in 45 % of cases. Average life expectancy is only 47.6 years-between 30 and 35 years lower than for the general French population. Medical care can only be fully effective if these patients' social and housing issues are dealt with too.