We report the clinico-pathological findings regarding a 9 year-old girl with some clinical features of Kleine-Levin syndrome who died suddenly as a result of pulmonary embolism in the course of femoro-iliac thrombophlebitis. Neuropathological examination provided evidence of perivascular inflammatory infiltrates and microglial proliferation of nodular type located in the diencephalon and midbrain. These findings suggest that a localized encephalitis may be the underlying condition in Kleine-Levin syndrome.