In an analysis of all singleton births and neonatal deaths with known birth weights and gestational ages in New York City maternity services during a three-year period (1976 to 1978), intensive care services at the hospital of birth were found to influence mortality only in preterm (less than 37 weeks' gestation) or low-birth-weight infants (less than 2251 g). By contrast, for infants who were born at term and of normal birth weight, mortality rates did not differ by level of perinatal care available at the hospital of birth. On the average, preterm and low-birth-weight infants were at a 24% higher risk of death if birth occurred outside of a level 3 center, regardless of whether birth occurred at a level 1 or level 2 hospital. Preterm and low-birth-weight infants, though constituting only 12% of births, accounted for 70% of neonatal deaths in New York City. The remaining infants, ie, those born at term and of normal birth weight, who experienced no measurable mortality advantage when born in a level 3 hospital, accounted for 88% of all births.