The prevalence of HIV infection in women at end of pregnancy, irrespective of outcome, was determined in a comprehensive survey of both women and medical centres during successive 4-week periods in four areas of the Paris region, France. Blood samples were tested anonymously for antibodies to human immunodeficiency virus (HIV)-1 and HIV-2. Of the 11,593 blood samples 0.40% (95% confidence interval [CI] 0.28-0.51) were positive for HIV-1 and 0.02% (95% binomial interval [BI] 0.002-0.065) for HIV-2. Seroprevalence was higher among women with ectopic pregnancy (2%) (95% BI 0.24-7.04); the rate in women having an elective or therapeutic abortion was more than twice that in those delivering babies (0.70% vs 0.28%, p less than 0.05, relative risk 2.54, 95% CI 1.36-4.75). Studies with neonatal HIV seroprevalence as a surrogate for HIV prevalence in pregnant women would underestimate prevalence in these women.