This publication reflects the interest and concern of the community of workers and scientists in the health field in the face of the problem caused by acquired immunodeficiency syndrome (AIDS) in the Region of the Americas. It constitutes what could be considered an epidemiologic mosiac of the similiarities and differences of AIDS and human immunodeficiency virus (HIV) infection in various countries and subregions of the Hemisphere. The North American experience, in which transmission among homosexuals and by contaminated needles and syringes predominates, contrasts with the rapid changes observed in the distribution of cases in the English-speaking Caribbean and Haiti, where an increasing number of women are affected by AIDS, and with the persistence of blood transmission in countries of Latin America. The first part of this publication provides a descriptive and analytic sample of the epidemiology of AIDS that-ranging from the northern to the southern end of the Hemisphere-comprises Canada, the United States of America, Mexico, Columbia, and Brazil, as well as Cuba and the English-speaking Caribbean. Interestingly, some of the articles not only document what has happened with the disease, but venture projections, derived from various premises and forecasting techniques, about the future of the epidemic. Withal, the consensus is that the problem will get considerably worse in the near future (Regional Adviser-PAHO).