The Kleine-Levin syndrome is a clinical entity characterized by recurring episodes of excessive eating, intermittent withdrawal sometimes amounting to excessive sleep, and behavior disorders of which uninhibited sexuality is the most specific. There are more than 20 recorded patients, all males and, with 1 exception, young. The ultimate prognosis is not firmly established but it appears to be good. The basic etiology is unknown, but there may be a distrubance of hypothalamic function. In the patient described the diurnal rhythm of electrolyte excretion was disturbed throughout 2 attacks.