To clarify the circadian rhythm of childbirths in Korea ,1673 cases of spontaneous vaginal delivery in comparison with 662cases of induced labors observed at the Korea University Medical Center during the two years between 1986 and 1987 are analysed in terms of the hour of the day at delivery. Whole cases comprise of 67.2 percents of nullipara and the remainder 32.8% parous women and 71.6 percent is represented by spontaneous vaginal delivery and 28.4% by induced labor of whole cases. Among spontaneous delivery, the ratio of the hour of delivery between A.M and P.M is approximately 6 to 4 and that between day-light time and night being 1 to 1. In contrast the ratios for induced labor are 4 to 6 and 6 to 4 respectively The peak time and the trough are the hour from midnight to 1: A.M and that from noon to 1: P.M which are coincided with the time immediately before retiring and lunch respectively. Although study cases categorized as spontaneous delivery, exogenous factors particularly arising from attendants appears intervening the circadian periodicity of childbirths.