The recurrent hypersomnia is a rare disorder and diagnosed by recurrent episodes of hypersomnia more than 18 hours a day lasting from several days to several weeks. The Kleine-Levin syndrome is a subtype of the recurrent hypersomnia and characterized by excessive eating or hypersexuality. I review the clinical features of recurrent hypersomnia comparing with our own two cases. The slight consciousness disturbance is seemed to cause the hypersomnic state. Several neurophysiological findings also support this hypothesis. Generally, the prognosis of this disorder is good. The psychophysical factor is seemed as a major factor to induce this disorder, therefore to reduce this factor is one of the most important treatment and the lithium carbonate is also useful as a pharmacotherapy. The mechanism of this disorder is still unknown.