With over 143,000 cases of AIDS reported to the World Health Organization from 145 countries and with an estimated 5 to 10 million people worldwide infected with HIV, AIDS has become firmly established as a global pandemic. In the region of the Americas over 100,862 cases of AIDS have been reported with indigenous transmission documented in 45 to 46 countries. While North America has the highest annual number of AIDS cases per population, with 72 cases/million, the Caribbean subregion has a disproportionately high number of cases, with annual rates as high as 200 to 300 cases/million population for some countries. Despite differences in absolute number of cases, there has been a remarkable similarity in the temporal rate of increase of AIDS in the countries of the Americas, reflecting delayed introduction of the virus to some areas with an early exponential increase similar to that observed initially in the United States. Although the modes of transmission of HIV are the same throughout the region, evidence of increasing bisexual and heterosexual transmission, particularly in the Caribbean subregion, has resulted in a lower male-to-female ratio of AIDS cases and increased perinatal transmission. Clinically, a resurgence of diarrheal diseases, respiratory infections, and tuberculosis has been documented in association with HIV infection in many tropical countries of the Americas. With relatively high rates of HTLV-I infection already established in the Caribbean subregion, the overall public health problems of the Americas will be markedly potentiated by further spread of these 2 human retroviruses. If HIV infection continues to penetrate the poor and less advantaged populations in Latin America and the Caribbean, the potential exists for a massive epidemic in the Americas that may rapidly parallel the situation in Africa.