The effect of the acquired immunodeficiency syndrome (AIDS) epidemic on women is substantial and warrants an updated analysis. To describe AIDS incidence trends in women. We analyzed national surveillance data on women 13 years of age and older with AIDS reported through June 1996. Data were adjusted for reporting delay, unreported risk, and the 1993 change in AIDS surveillance case definition to assess overall trends and examine trends by age group and birth cohort. Surveillance conducted by the Centers for Disease Control and Prevention in collaboration with state and local health departments. In 1995, women accounted for 19% of AIDS cases in adults; AIDS incidence rates per 100000 women were highest in black women (50.1), women in the Northeast (22.3), heterosexual contacts (5.5), and women living in metropolitan statistical areas with more than 1 million residents (15.9). Greatest increases in rates between 1991 and 1995 by region and mode of transmission were in the South and in heterosexual contacts. Greatest increases in AIDS incidence rates were observed in heterosexually infected women born between 1970 and 1974, ie, women who were 14 to 18 years old in 1988. These trends predict continued growth of the number of AIDS cases in women, especially in those in the South and those infected heterosexually, and suggest that successive cohorts of young women may be at risk for human immunodeficiency virus infection as they reach adolescence and young adulthood. Prevention programs must reach young women before they initiate sexual activity and drug use.