We report a 2-year-old boy who developed hemiconvulsion-hemiplegia syndrome with left-sided hemiplegia after a seizure lasting 35 minutes. The interleukin-6 level in the cerebrospinal fluid 2 hours after seizure onset was elevated to levels seen in patients with encephalitis. At 1 year after onset of the seizure, the patient remained hemiplegic on the left side, and magnetic resonance imaging showed severe right hemispheric atrophy. Acute changes seen on imaging studies and electroencephalograms in this patient were consistent with seizure-induced brain damage. Elevation of cerebrospinal fluid interleukin-6 may be related to the severe neurologic sequelae of our patient despite the relatively short seizure duration.