Neonatal respiratory distress syndrome (RDS) is an important complication of elective repeat cesarean section. In a review of 68,880 consecutive deliveries, 1,897 women underwent elective cesarean section at a gestation estimated to be greater than or equal to 38 weeks. Seventy-one (4.3%) of the infants of the 1,649 women who were not in labor at the time of delivery developed neonatal RDS. None of the infants of the 248 women who were in spontaneous labor at the time of delivery developed RDS (P less than 0.005). There were no cases of uterine rupture in either group. Of the 71 infants who developed RDS, 29 (41%) were judged to be at term on the basis of both examination and birth weight. Misapplication of fetal ultrasound data contributed to the premature delivery of more than one third of the infants with RDS. Awaiting the onset of spontaneous labor to determine the timing of repeat cesarean section in women at term is an effective way to preventing iatrogenic neonatal RDS.