A seroepidemiologic study of herpes simplex virus (HSV) in Okinawa was performed. A total of 423 serum samples were collected from all over Okinawa, and the positivity rate of antibody against HSV was measured using a passive hemagglutination method. The sero positive rate for HSV in age groups of over 40 years was 100%. Seven HSV type 2 (HSV 2) isolates were obtained in Okinawa, and DNA preparations from Vero cells infected with the isolates were analyzed using five restriction endonucleases: Bam HI, Hind III, Kpn I, Bgl II and Eco Rl. Variations in the genomic region were demonstrated in five of the isolates. Such variations have not been reported previously in HSV 2 in mainland Japan. This is the first report of a seroepidemiologic study of HSV and restriction endonuclease cleavage analysis of HSV 2 in Okinawa, is a subtropical island where HSV is endemic. Acta Pathol Jpn 41: 24–30, 1991.