A prospective cohort study of 318 human immunodeficiency virus 1 (HIV-1)-infected and 309 seronegative pregnant women was carried out in Butare, Rwanda. Birth weight was significantly lower among singleton infants born alive to HIV-1-infected mothers compared with those born alive to seronegative mothers (2706 g vs. 2825 g; P = 0.002). Crown-to-heel length, head circumference, chest circumference and placental weight were also reduced. Maternal HIV-1 infection was significantly associated with intrauterine growth retardation but not with preterm birth. Differences in the body mass index and weight/head ratio suggest that the adverse impact on live born infants may have been most severe towards the end of pregnancy, resulting in a lean infant with a relatively large head. The higher frequency of intrauterine growth retardation could not be explained by potential confounding factors such as maternal cigarette smoking, history of sexually transmitted diseases or sociodemographic characteristics. The neonatal physical examination did not reveal any differences in clinical signs or symptoms within 48 hours of birth except for the presence of conjunctivitis which was more common among infants of HIV-1-infected mothers. The perinatal and neonatal mortality rates were not significantly affected by maternal HIV-1 status.