Little information is available on the prevalence of herpes simplex type-2 (HSV-2) antibodies among groups at potential high risk of HIV in Asia. This study was carried out to determine the prevalence of HSV-2 antibodies and correlates of HSV-2 infection in female sex workers (FSWs) in border provinces of Vietnam. Nine hundred and four FSWs in five border provinces of Vietnam were interviewed about selected sociodemographic and behavioural characteristics, and information about partners by a standard interview schedule. Serological samples were collected for HSV-2 antibodies, syphilis and HIV. The overall prevalence of HSV-2 antibodies was 27.7% (95% confidence interval [CI]: 24.8-30.7%). The prevalence of HSV-2 in southern provinces (Dong Thap 32.3%, An Giang 33.3% and Kien Giang 29.9%) was higher than that in the central (Quang Tri 20.8%) and northern border areas (Lai Chau 5.0%). In multivariate analysis, Kinh ethnicity (odds ratio [OR] = 2.59, P = 0.02), direct sex work (OR = 1.61, P = 0.01), >/=9 clients/week (OR = 2.11, P = <0.001), ever worked outside Vietnam (OR = 2.12, P = 0.05), >1 pregnancy termination (OR = 1.58, P = 0.05), syphilis (OR = 5.19, P = <0.001) and HIV (OR = 2.68,P = 0.01) were associated with HSV-2. Age </=20 (OR = 0.65, P = 0.05) and current oral contraceptive use (OR = 0.55, P = 0.01) were protective for HSV-2 antibodies. A significant proportion of FSWs in border provinces have HSV-2 antibodies, more so in the southern region. FSWs should be educated about recognition of signs and symptoms of genital herpes and the role this infection has in facilitating HIV transmission.