The objective of this study was to determine the seroprevalence of herpes simplex virus type 2 (HSV-2), and to evaluate the relationship between HSV-2 infection and sociodemographic factors and the sexual practices of female sex workers (FSWs) in Kaiyuan city, Yunnan Province, China. This cross-sectional study involved 737 FSWs and was carried out from March to May 2006 with confidential interviews and laboratory tests for HSV-2 and other sexually transmitted infections (STI). HSV-2 was the most common STI (68%), followed by Chlamydia trachomatis (26%), Trichomonas vaginalis (11%), Neisseria gonorrhoeae (8%) and syphilis (7%). Prevalence of HIV-1 was 10.3%. Adjusted odds ratios of HSV-2 seroprevalence were 2.6 (95% CI [confidence interval]: 1.30-5.38) for HIV-1 infection, 2.0 (95% CI: 1.33-3.16) for vaginal douching, 2.0 (95% CI: 0.45-0.86) for condom breaking or falling off during sexual intercourse with the client in the previous week, 1.8 (95% CI: 1.07-3.18) for > or =5 years of commercial sex work, 1.6 (95% CI: 1.08-2.33) for > or =5 clients in the previous week, 0.6 (95% CI: 0.45-0.86) for > or =9 years of education. This study identifies a very high prevalence of HSV-2 infections among FSWs in Yunnan Province, with only a few who reported a prior history of genital herpes. HSV-2 serological screening and suppressive therapy should be considered for study populations. Education on the importance of diagnosis, treatment and prevention may help control the spread of HSV-2 infection.