Neonatal mortality, idiopathic respiratory distress syndrome, and early periventricular/intraventricular hemorrhage in the neonate weighing 2000 g or less were correlated with umbilical artery acid-base status. Neonatal mortality and, to a lesser extent, idiopathic respiratory distress syndrome correlated with umbilical artery acidosis. Early periventricular/intraventricular hemorrhage was associated with low Apgar scores, but showed no correlation with umbilical artery acid-base status.