BACKGROUND: Identification of risk factors for sexually transmitted diseases (STDs) assists in development of treatment algorithms, which are potentially important components of STD control when microbiologic facilities are limited. METHODS: A cross-sectional study was performed to assess STD and HIV risk factors of 2285 women attending three family planning clinics in Dar-es-Salaam, Tanzania during 1991-92. Women were interviewed and examined for signs of STDs. Specimens were taken for laboratory diagnosis of HIV, other sexually transmitted organisms, and Candida albicans. RESULTS: The prevalence of gonorrhoea was found to be 4.2%, prevalence of trichomoniasis was 14.3%, and positive syphilis serology was found in 2.5% of women. Unmarried women were at increased risk of trichomoniasis (age-adjusted OR = 1.48 95% CI [1.12, 1.95]), gonorrhoea (age-adjusted OR = 1.81 95% CI [1.14, 2.86]) and syphilis (age-adjusted OR 1.5 [0.84, 2.68]). An increasing number of sexual partners in the past five years was associated with an increased risk of all STDs. Current use of the oral contraceptive pill was positively associated with gonorrhoea, multivariate OR = 1.75 95% CI [1.05, 2.93]. The prevalence of candidiasis was 11.5% and was not associated with any of the demographic or behavioural risk factors examined. Clinical diagnostic algorithms for STDs in this study population had relatively low sensitivity and low positive predictive value. CONCLUSION: Being unmarried and having a higher number of sexual partners were consistently associated with each STD, while the associations for other risk factors varied between STDs, emphasising the complexity of STD distribution. Further development of diagnostic algorithms and other methods for screening women for STDs are needed to reduce the impact of STDs and HIV in developing countries.