The results of the Newborn HIV Seroprevalence Study in New York State for 1988 were used to estimate the number of human immunodeficiency virus (HIV)-infected women of childbearing age in 1988. The estimate was accomplished for each of 80 age, racial/ethnic, and geographic strata by dividing the number of seropositive newborns by the 1988 estimated fertility rate. Summing across strata yielded a total of 23,430 infected women age 15 to 44 years in 1988. From this estimate a tree model was used to estimate the number of women infected during 1981-88. Back calculation was used to distribute these infections over time, and the selected incubation distribution was used to estimate future AIDS cases for this population: 8,295 cases by 1993.