OBJECTIVES: To assess the feasibility of collecting sexual behaviour data during HIV surveillance in antenatal care (ANC) clinics, and to establish whether these data can provide information about the correlates of HIV infection in this population. METHODS: Sexual behaviour surveys were conducted in the context of two HIV sentinel surveillance rounds in 11 ANC clinics in north west Tanzania between 2000 and 2002. Responses of individual women were anonymously linked to their HIV status. Three clinic catchment areas overlapped with a community based longitudinal study, which provided independent estimates of HIV prevalence and sexual behaviour. Changes between rounds and differentials between clinics were assessed and a two level logistic regression model used to identify behavioural and contextual correlates of HIV in 3689 women under 25 years of age. RESULTS: Women attending clinics were willing to participate in the study. The sexual behaviour data obtained were internally consistent and tallied reasonably well with sexual behaviour data collected in the community overlapping the clinic catchment. Clear relations emerged between HIV infection and measures of sexual exposure: OR 1.20 (95% CL 1.12 to 1.28) for each year of premarital exposure and 1.09 (1.04 to 1.16) for each year after first marriage; background prevalence OR 1.15 (1.04 to 1.26) associated with each percentage point increase in background prevalence at the clinic; and certain partnership variables such as partner's age OR 0.58 (0.45 to 0.76) if partner less than 10 years older. CONCLUSION: Conducting sexual behaviour surveys in the context of ANC clinics surveillance is feasible and yields useful data.