We present a review of epidemiologic data collected by Projet RETRO-CI between 1987 and 1993 on trends in human immunodeficiency virus type 1 (HIV-1) and HIV-2 infections and on cases of AIDS in Abidjan, Côte d'Ivoire. Overall rates of HIV infection in pregnant women had already reached 10% in 1987, and have increased only modestly since then. In contrast, in 1992-1993, rates in men with sexually transmitted diseases and in female commercial sex workers reached 27 and 86%, respectively. The increases in infection rates have been largely due to transmission of HIV-1, whereas rates of HIV-2 have remained stable or have declined. Among persons with tuberculosis and hospitalized patients, rates of 46-71% have been reached, increases in recent years again being largely attributable to HIV-1. Among the 15,245 AIDS cases reported by Projet RETRO-CI, a steady decline in the male:female sex ratio has occurred over time, from 4.8:1 in 1988 to 1.9:1 in 1993. It is likely that AIDS cases were initially concentrated among a core group of female commercial sex workers and their male clients. A substantial proportion of sex workers and their clients originate from neighboring countries, and migration is likely to have contributed to the spread of HIV infection in West Africa. Including HIV-associated pulmonary tuberculosis as an AIDS-defining illness increased AIDS cases reported by Projet RETRO-CI by 13% in 1993. Despite a need for interventional research, careful description of the evolution of HIV/AIDS in this region remains essential.