AIDS was first recognized in the spring of 1981, when the Center for Disease Control (CDC) received reports of multiple cases of two rare diseases occurring in young, previously healthy, homosexual men from New York City and California. These patients had a specific impairment in the cell-mediated component of the immune system, and they developed diseases predictive of this impairment. Cases of AIDS in adults can be divided into six patient categories that suggest a possible means of disease acquisition: (1) 73 percent are homosexual or bisexual men, (2) 17 percent are past or present abusers of intravenous (IV) drugs, (3) 8 percent are both homosexual/bisexual and IV drug abusers, (4) 1 percent are hemophiliacs, (5) 1 percent were heterosexual partners of persons in one of the first three groups, and (6) 2 percent were recipients of single-donor blood transfusions. Fifty-one percent of patients are reported to have died. Ninety percent of AIDS patients are between the ages of 20 and 49; 47 percent are between 30 and 39 years old. There are reports of 416 children under the age of 13 with pediatric AIDS. The risk factors of HIV transmission are homosexuality, IV drug use, blood transfusions, heterosexual transmission, and other factors, (such as persons born in Haiti or central Africa). 4 exhibits, 2 tables, and 42 references.