The prevalence of human immunodeficiency virus (HIV) infection was determined in women at the time of childbirth throughout New York State between November 30, 1987, and November 30, 1988. Mandatory blood specimens (276,609) obtained from all newborns were examined for HIV. The overall HIV seroprevalence rate was 0.66% (1816 newborns), with 0.16% in Upstate New York and 1.25% in New York City. Rates for newborns whose mothers were aged 20 to 29 years (1.30%) and 30 to 39 years (1.35%) were significantly higher than rates for those with mothers younger than 20 years of age (0.72%). Rates of seropositivity were higher among blacks (1.8%) and Hispanics (1.3%) than among whites (0.13%). Seropositivity of HIV was higher in zip code areas with high rates of drug use (2.2%) than in the rest of New York City (0.8%). It is estimated that more than 726 HIV-infected children were born in New York State during the 1-year study period, using 40% as the probable proportion of seropositives that will become infected.