OBJECTIVE To estimate human immunodeficiency virus (HIV) type I prevalence among childbearing women, HIV incidence in infants, and the number of children living with HIV infection and acquired immunodeficiency syndrome as a result of transmission from mother to infant (vertical transmission). METHODS The national HIV serosurvey of childbearing women was used to estimate the incidence of vertically acquired HIV infection in children born between 1988 and 1993. Data from the national acquired immunodeficiency syndrome case surveillance system and a multicenter pediatric HIV surveillance project were modeled to estimate incidence in children born between 1978 and 1987. METHODS Surveillance conducted by the Centers for Disease Control and Prevention, Atlanta, Ga, in collaboration with state and local health departments. RESULTS Approximately 14,920 HIV-infected infants were born in the United States between 1978 and 1993. Of these, an estimated 12,240 children were living at the beginning of 1994; 26% were younger than 2 years, 35% were aged 2 to 4 years, and 39% were aged 5 years or older. Approximately 6530 HIV-infected women gave birth in the United States in 1993, and, based on a 25% vertical transmission rate, an estimated 1630 of their infants were HIV infected. CONCLUSIONS These results provide a basis for estimating medical and other resource needs for HIV-infected women and their children and for measuring the impact of interventions to reduce vertical transmission of HIV.