We report a 63-year-old Japanese man with epilepsy who developed skin eruptions, liver dysfunction, high fever, leukocytosis and atypical lymphocytosis 4 weeks after he had started taking carbamazepine. Titers of human herpesvirus 7 (HHV-7)-specific IgG antibodies were significantly increased and HHV-7 DNA was detected in his serum by polymerase chain reaction. These findings suggested that reactivation of HHV-7 could contribute to the development of drug-induced hypersensitivity syndrome.