We describe our experience at Jackson Memorial Hospital in Miami, Florida, with 172 children who were given diagnoses of perinatally acquired infection with human immunodeficiency virus type 1 (HIV-1). The 146 mothers of the children acquired HIV-1 through heterosexual contact (69 percent), intravenous drug use (30 percent), or blood transfusion (1 percent). The children presented with symptomatic disease at a median age of eight months; only 21 percent presented after the age of two years. The most common first manifestations of disease were lymphoid interstitial pneumonia (in 17 percent), encephalopathy (in 12 percent), recurrent bacterial infections (in 10 percent), and candida esophagitis (in 8 percent), for which the median survival times from diagnosis were 72, 11, 50, and 12 months, respectively. Nine percent of the children had Pneumocystis carinii pneumonia at a median age of five months and had a median survival of only one month. The median survival for all 172 children was 38 months from the time of diagnosis. Mortality was highest in the first year of life (17 percent), and by proportional-hazard analysis the probability of long-term survival is low. In multivariate analyses, early age at diagnosis and the first identifiable pattern of clinical disease were found to be independently related to survival. We conclude that children with perinatally acquired HIV-1 infection have a very poor prognosis and that most become symptomatic before one year of age. Early diagnosis is important, since there is only a short interval in which to initiate prophylactic or antiviral treatment before progressive disease begins.