From January 1998 to December 2004, 207 out of 1125 samples were HSV isolation positive and typed. Two groups of patients, Thai and foreigner, as well as site of infection, non-genital and genital area, were identified. The prevalence of non-genital HSV-1 infection from 27 samples of Thai patients was 81.84%. Out of 180 genital samples, 39.02% HSV-1 and 43.09% HSV-2 from 123 Thai patients and 36.84% HSV-1 and 49.12% HSV-2 of 57 foreigner patients were determined. Moreover mixed infection of HSV-1 and HSV-2 was found in both Thai and foreigner groups, 17.89% and 14.04%, respectively. The prevalence of genital HSV-1 infection in Thai patients chronologically increases from 1.6% to 56.91% from of 1985 to 2004. Increase of HSV-1 genital infection and mixed HSV-1 and HSV-2 infection in Thai people might probably be due to changing of sexual behavior in the AIDS era.