To investigate potential adverse effects of residency training on pregnancy outcome, a cohort study was conducted among 45 university-affiliated residency programs. Outcomes of the first pregnancy experienced during residency were compared between 92 female residents and 144 spouses of male residents. Despite long hours, sleep deprivation, and an increase in perceived stress, the female residents were as likely to give birth to a live, full-term newborn as the spouses of male residents. For white cohort members, an increased risk of premature labor without delivery was identified (RR = 12.3, 95% confidence interval 2.4-61.6). No significant differences were found in prematurity, spontaneous and therapeutic abortions, or presence of congenital abnormalities in the infants. Method of delivery and use of anesthetics and of other medications were similar in both groups. Pregnancy outcomes between the two groups were similar; however, the increased risk for premature labor among female residents is a cause for concern and should be further investigated.