Antibodies to HIV were found in blood and tissue samples as early as 1969. Retrospectively, it is believed that there may have been sporadic cases of the disease in the United States since 1965. The clinical syndrome of AIDS was first recognized among gay men in San Francisco and New York in 1981. The isolated cases of Kaposi’s sarcoma and uncontrollable infections with normally nonpathogenic organisms were quickly recognized to be part of a single pathologic process. This identification was possible because the syndrome occurred in a subpopulation that was easily recognizable and well known to venereologists and infectious disease experts. Had an equally small number of cases been diluted in the general population, it might have taken several more years to recognize that AIDS was an epidemic infectious disease.