We used national AIDS surveillance data to characterize trends in the numbers and proportions of heterosexually acquired AIDS cases diagnosed from January 1988 through December 1995 among adults and adolescents. We adjusted for expansion of the 1993 AIDS surveillance case definition and for delays in reporting, and we redistributed cases initially reported without risk. The chi-square test for linear trend was used to analyze trends at the p < 0.01 level by half-year of diagnosis and by sex, age, race or ethnicity, geographic region of residence at diagnosis, and partner's HIV exposure risk. From 1988 through 1995, heterosexual contact accounted for 10% of all AIDS cases. Heterosexual contact increased the most rapidly of all HIV exposure modes, with increases found among men and women in all age groups; among blacks, whites, and Hispanics: and among persons living in all geographic regions of the country. Blacks and Hispanics accounted for 75% of all persons reported with AIDS attributed to heterosexual contact. Although heterosexual contact with an injection drug user (IDU) accounted for most cases until 1993, cases increased most rapidly among persons reporting heterosexual contact with an HIV-infected partner whose risk was not specified. Findings suggest continued growth of the heterosexual AIDS epidemic. Because of the disproportionate and increasing number of heterosexually acquired AIDS cases among blacks and Hispanics, black and Hispanic communities at risk for HIV infection should be considered a high priority for prevention and education programs specifically targeting heterosexually active adolescents and adults. Epidemiologic and behavioral research and prevention program evaluation are urgent public health priorities to better control and prevent the further spread of HIV among heterosexually active adults and adolescents.