PIP: In less than a decade, AIDS has spread throughout Africa. The authors review what is known about the current situation of HIV infection in Africa, with emphasis upon sub-Saharan Africa, and identify questions and challenges for AIDS control and prevention in the 1990s. Well-conducted random cluster surveys have shown that in some urban centers as many as one adult in three is infected, but that in other countries less than 1% of the population is infected. There are many different HIV/AIDS epidemics interwoven across the continent, although the prevailing modes of HIV transmission are identical throughout Africa. Patterns of behavior vary widely across Africa. There are major differences between and even within African countries in the rate of spread of HIV, the level of presumed stabilized seroprevalence rate, the male-to-female ratio of AIDS cases and the number of people with HIV infection, the spread of the epidemic to rural areas, and the socioeconomic groups involved. Many different behavioral, biological, and social factors explain this heterogeneity. It remains clear, however, that AIDS is exacting a heavy toll upon many African populations. Even in a city as recently affected as Abidjan, AIDS has become the leading cause of death in adult men, and second only to deaths related to pregnancy and abortion in women. The vast majority of Africans infected with HIV remain deprived not only of any antiretroviral therapy, but also of treatment of many opportunistic infections and sometimes of the most basic care. Community support for AIDS patients is developing in a few areas with large numbers of cases.