Kleine-Levin syndrome belongs to the recurrent hypersomnias group. It is a rare and benignant disease, occurring in young men 10 to 25 years old. The diagnosis is first clinical and the hypersomniac episodes, joined to psychiatric symptoms, are irregularly recurrent during few years. Diagnosis is uneasy during the first episode and in the attenuated forms... 500 cases have been described all around the world but it's highly likely that many patients haven't been listed. This syndrome, just like Gélineau disease, stands in the group of primary pathological hypersomnias. In a clinical point of view, the cardinal and constant symptom is hypersomnia. Psychiatric symptoms can be irregularly joined: megaphagia, sexual behavioural disorders, thymic disorders, personality modifications. The clinical examination is poor and aspecific. During an hypersomniac episode, a polygraphic recording during 24 or 48 hours will give diagnosis informations (fragmented and unstable sleep, reduction in stages 3 and 4 of non-REM sleep, reduction in REM sleep latency) and a biological and radiological evaluation will be necessary to exclude organic etiology (tumoral progres, infectious disease...). In a therapeutic point of view, prescription of psychostimulant drugs is recommended during fits and some treatments are used in a preventive way (lithium and carbamazepine).