OBJECTIVES: To study the epidemiological trends, clinical patterns, evolution and prognosis of HIV infection in women. DESIGN: Cohort study of 1816 HIV-infected patients. RESULTS: Up to 1 January 1991, 483 (26.6%) of the patients reported to the Groupe d'Epidemiologie Clinique du SIDA en Aquitaine surveillance system were women. The male-to-female ratio has decreased progressively (3.4:1 in 1985; 2.7:1 in 1990) over time. Fifty per cent of HIV-infected women are or have been intravenous drug users (IVDU). The proportion of heterosexually acquired HIV infection increased from 11.6 to 34.6% over the last 5 years; 46.9% of the women infected through heterosexual intercourse reported sexual contacts with male IVDU. Excluding Kaposi's sarcoma, no significant difference was observed between men and women in the overall distribution of AIDS-defining events. The observed trend of a slower progression to AIDS in women, compared with men, disappeared when controlling for prognostic variables. However, female sex significantly enhanced survival after AIDS diagnosis in multivariate analysis (relative risk, 2.7; 95% confidence interval, 1.1-6.2). CONCLUSION: Early diagnosis of HIV infection in female patients and prevention of HIV infection among women is now a priority for public health interventions, both in industrialized and in developing countries.