In order to evaluate the effect of cesarean section on reduction of perinatal mortality rate (PMR). All cases delivered in Beijing Obstetrics and Gynecology Hospital from Jan. 1, 1980 to Dec. 31, 1992 were analysed. The total number of delivery in study period was 74,199. Number of cesarean section delivery was 18,557. The cesarean section rate was 25.0%. The total number of perinatal baby was 74,914. The number of perinatal death was 1,140. PMR was 15.2%. The 13 years were divided into three periods to compare the cesarean section rate and PMR. The 1st period was from 1980 to 1984. The 2nd period was from 1985 to 1988. Years from 1989 to 1992 were 3rd period. The cesarean section rate was increasing year by year. It was significant since 1985. On the other hand, the PMR was marked decreasing since 1983. But there was no continually decrease in 2nd period. In 3rd period trend of decreasing PMR was shown. There was no significant difference in PMR especially in neonatal mortality rate (NMR) between cesarean section group and vaginal delivery group in 1st period. In 2nd period the PMR and NMR of cesarean section group was higher than that of vaginal delivery group (P < 0.01). In 3rd period it was lower in cesarean section group (P < 0.05). Main causes of neonatal deaths in cesarean section group were congenital abnormalities and respiratory diseases. In 2nd period pulmonary hemorrhage, hyaline membrane disease were marked higher in cesarean section group. It was related to more premature and low birth weight babies in this group.(ABSTRACT TRUNCATED AT 250 WORDS)