About 1.5 million Americans are already infected with the HIV virus, but not all will develop AIDS. Most of those affected in the near future will be homosexual men or intravenous drug abusers, and a significant proportion of them will be Blacks and Hispanics. By 1992, there will probably be 365,000 AIDS cases in the United States. The first national AIDS case control study, conducted in 1981 among homosexual men, indicated the variable that most clearly distinguished patients with the disease from homosexual controls was the number and frequency of sexual contacts. Another study in 1982 provided further evidence that AIDS was transmitted through sexual relations among homosexually active men. Also in 1982, AIDS cases were found among people who had been injected with blood or blood products. In 1983, two well-documented AIDS cases among heterosexual partners of male intravenous drug abusers were reported. As of July 1988, 66,464 adults and children had AIDS; 63 percent of the victims are homosexual or bisexual men with no history of intravenous drug abuse. Members of the fastest growing group of reported AIDS patients are children. The geographic distribution of AIDS shows the Northeast to be most affected. The disproportionate percentage of AIDS cases among Blacks and Hispanics largely reflects higher reported rates of AIDS in Black and Hispanic intravenous drug abusers, their sex partners, and their infants. It appears that some infected individuals may be more efficient transmitters of HIV than others and that a person's infectiousness may vary with time. The strategy for controlling HIV infection and AIDS involves educating people on how to avoid behavior that results in the transmission of HIV. 8 figures.