The prevalence of HIV-1 among women of reproductive age is currently estimated at the time they give birth. We assessed HIV-1 prevalence at the end of pregnancy, whether they delivered or had an induced or spontaneous abortion. Women admitted at the end of pregnancy to hospitals in the Lazio Region, Italy, were tested for antibodies to HIV-1. Consent for testing was granted by 97.1% of 218,357 subjects; women who did not consent were tested anonymously. The prevalences of infection were 0.34% in 1989, 0.38% in 1990, 0.28% in 1991, 0.23% in 1992, 0.28% in 1993, and 0.24% in 1994. Significantly higher prevalences of infection were associated with induced abortion (0.49%) than with delivery (0.18%; OR: 2.72; 95% CI: 2.29-3.22) and among women who refused (0.85%) than among those who consented to testing (0.27%; OR: 3.14; 95% CI: 2.35-4.19). A significant temporal reduction in prevalence was observed only among women who delivered (0.15% in 1993 and 1994; 0.26% in 1989 and 1990). The prevalence of HIV-1 infection is thus higher among women undergoing induced abortions than among those who deliver and higher among women who refuse testing than among those who consent. Studies confined to neonatal testing or to voluntary testing of pregnant women would thus underestimate the prevalence of HIV-1 among women of reproductive age.