The Kleine-Levin syndrome (KLS) is characterized by periodic, sudden-onset episodes of hypersomnia, compulsive hyperphagia, and behavioral-emotional symptoms, lasting from a few days to a few weeks, with complete remission in the intercritical periods. We report on efficacy of lithium treatment in a highly recurring form of the disorder in a 17-year-old male adolescent. The decreasing severity of the disorder paralleled the progressive increase of lithium dosage, up to 0.9 mEq l(-1). Implications regarding the pharmacological treatment of this neglected disorder are discussed.