INTRODUCTION: Kleine Levin syndrome is an infrequent disorder of uncertain aetiopathogenesis that usually affects adolescent males, producing drowsiness and alterations in behaviour, appetite and sexuality. We report a clinically typical case in which the brain SPECT showed right frontal hypoperfusion. CASE REPORT: Male aged 17, right handed, who presented drowsiness, apathy, alterations in his sexual behaviour (masturbations in public and attempted assault of women) and hyperphagia, which coincided with his undergoing an emotionally stressful period in his life. Brain SPECT revealed reduced flow in the right frontal lobe, although MRI and CSF study were normal. The polysomnographic study revealed a destructured pattern of sleep, with a reduction in phases III and IV and in REM sleep. He was treated with lithium and evolved favourably without any relapses during the 18 month follow up. CONCLUSIONS: Cases of Kleine Levin syndrome with structural lesions have been reported, but most of them are idiopathic. A disorder in the hypothalamus and the limbic system is suggested. In our case, the findings from the brain SPECT confirmed a non dominant hypoperfusion of the frontal lobe, which could result from a phenomenon of diaschisis brought about by a diencephalic dysfunction.