Introduction Sexually transmitted infections (STIs) continue to be a major concern in public health because of their high incidence and prevalence. STIs are also a major problem for FSWs in Vietnam. The purpose of the research is to determine the prevalence of STIs and risk-related factors in Ba Ria – Vung Tau, Vietnam.

Methods Data were collected using a cross-sectional survey of 420 direct and indirect FSWs between January–May, 2014, from 2 cities and 6 districts in Ba Ria – Vung Tau. FSWs were interviewed using a structured questionnaire and biological samples taken and tested for HIV. A database was created using Epidata 3.1 software and analysed using the SPSS 20.0 statistical package. Univariate and multivariate analyses were used to investigate the associations between STIs and risk-related factors.

Results Prevalence were 6.9% for Syphilis, 7.9% for Gonorrhoea (GC), 16.4% for Chlamydia (CT) and 21.4% for any one of the STIs (GC/CT). Increased risks for GC/CT were associated with age of first sexual intercourse ≤18 (OR 3.57, 95% CI: 2.11–6.06, p = 0.011); number of paying clients in the past month >15 (OR = 2.16, 95% CI: 1.34–3.46, p = 0.001); inconsistent condom use with regular customers (OR = 1.98, 95% CI: 1.17–3.37, p = 0.010) and new customers (OR = 2.18, 95% CI: 1.20–3.94, p = 0.009); and unprotected sex with non-paying partners (OR = 3.89, 95% CI: 1.51–10.00, p = 0.003). A higher likelihood of Syphilis was significantly associated with having anal sex (OR = 3.14, 95% CI: 1.25–7.85, p = 0.010).

Conclusion The prevalence of STIs is high among FSWs in Ba Ria–Vung Tau, Vietnam. Therefore, the existing STIs treatment and intervention programs should be reviewed and if necessary modified or strengthened to reduce the risk of infection. Health education, especially relevant to the risk-related factors observed in the study should be improved and 100% condom use program should be implemented.