A 22 year-old woman suffered from recurrent episodes of hypersomnia, apathy, and hyperphagia. The symptoms occurred 3 to 4 times per year, and each attack lasted 2 to 3 weeks. 99mTc-ethylcysteinate dimer brain single photon emission computed tomography (SPECT) was performed during symptomatic and asymptomatic periods. To localize brain regions with perfusion changes during symptomatic period, asymptomatic SPECT was subtracted from symptomatic SPECT. The subtracted SPECT showed significant hypoperfusion in the left hypothalamus, bilateral thalami, basal ganglia, bilateral medial and dorsolateral frontal regions, and left temporal lobe during the symptomatic period. These cerebral hypoperfusion areas support the diencephalic hypothesis and clinical symptoms of Kleine-Levin syndrome.