• Adolescents engaging in certain sexual or drug-related behavior are at risk of contracting the human immunodeficiency virus infection in endemic locales. Local and national surveillance data were analyzed to determine the characteristics of the acquired immunodeficiency syndrome (AIDS) epidemic on adolescents. Of the 605 cases of AIDS in people aged 13 to 21 years reported through 1987, 518 were males (83 from New York City [NYC], NY), and 87 were females (28 from NYC). Over half of all adolescent males with AIDS reported homosexual contact. Transfusion/blood product-related human immunodeficiency virus acquisitions (especially in males with hemophilia) represented 11% of adolescent cases from NYC (1% of NYC adults) and 22% of adolescent cases in the United States (US) outside of NYC (4% of adults in the US). Intravenous drug use was more frequently reported among adolescents with AIDS from NYC (23%) than among adolescents outside NYC (14%). In females, heterosexual transmission accounts for about half of all adolescent AIDS cases and 29% of all adult cases. Age-appropriate services and behavioral interventions are urgently needed for high-risk adolescents.