Anorexia nervosa is a disease that affects both mental and physical health. The most severe forms as they require long hospital care, with a drop-out rate very high (20% of adolescents and 60% of adults) are those with the worst prognosis. But this drop-out (or early exit) generates both relapse and a chronicisation. If the long-term outcome of these patients is documented, studies focusing on the most severe forms are few, and among them, those taking into account both the somatic and psychic aspects of their outcome are almost nonexistent. That’s why, after focusing on epidemiological data on anorexia nervosa, we chose to focus our thesis on first the search for factors explaining the drop-out and may become therapeutic targets, and second the physical and psychological outcome of these subjects ten years after hospitalization.The first study of 180 patients from ten centers taking care of severe anorexic patients, relied on a prospective clinical multicenter epidemiological study called EVALHOSPITAM. Our objective was to identify predictors of drop-out during hospitalization for anorexia nervosa. Indeed, taking into account such factors upon admission might help reduce drop-out during hospitalization, and thus help to improve the prognosis of these subjects.The second study presents the results of an outcome study of patients hospitalized during adolescence on average nine years before. Our work focuses on the somatic outcome of long-term patients who suffered from anorexia nervosa, its link to psychiatric outcome and finally a comparison with a sample from the general population of the same age and sex.