[Epidemiological studies based on medical and administrative databases : a potential strength in France].

Population-based epidemiological cohorts may include nowadays hundreds of thousands of subjects, followed-up during decades. France has a major potential strength: nationwide medical and social databases set up for administrative purposes. The main databases useful for epidemiology are the social security database which contains individual medical data from different sources, and the retirement fund database on employment and social benefits. These databases have several advantages: they cover the whole French population, with no lost to follow-up, data are often of good quality and it is possible to link them with individual surveys. However medical data are not always ascertained and an important methodological and practical work has to be done, and some legal and practical problems have to be solved for an optimal use.