Recurring hypersomnias are described according to 3 etiological groups: 1) idiopathic - the Kleine Levin syndrome and its clinical variants - 2) organic and 3) psychiatric. The typical form of the Kleine Levin syndrome is remarkable for the association of recurring episodes of sleep, overeating and temporary mental disturbances lasting from a few hours to several days. Its diagnosis is mainly based on clinical data Laboratory investigations have so far failed to document specific features. Emphasis is laid on circumstances at onset and pathological studies which could be in favour of a viral origin. Some clinical aspects and polysomnographic features are reminiscent of endogenous depression. The treatments of hypersomniac episodes based on stimulants are often disappointing. On the other hand, the prevention of the hypersomniac episodes of the Kleine Levin syndrome with lithium carbonate has been successful in several well-documented cases as well as the prevention of the hypersomniac episodes of the menstruation related hypersomnia with ovulatory inhibitors. Organic and psychiatric forms of recurring hypersomnias are not well known. Their clinical features are described and their various possible etiologies indicated.