In order to study twin pregnancies, a retrospective survey was carried out in Yonsei University, Severance Hospital. Twin deliveries during 1967-1976 numbered altogether 264, and their relative frequency was 1.30%. Clinical palpation in addition to auscultation and roentgenologic technique had been used in the twin diagnosis. The diagnosis was made prior to delivery in 93.18% of the cases. The deliveries took place in the 37.26th (S.D. 3.95) gestational weeks on an average. The mean weights of the infants were-A (first baby) 2416.03g. (S.D. 802.61), and B (second baby) 2299.81g. (S.D. 190.31). The most common manner of twin delivery was spontaneous vaginal delivery. Cesarean section was done in 14.39%, of which the most common indication was hypotonic uterine dysfunction (34.21 %). Low one minute Apgar scores occured more often in B twins than among A twins. Breech delivery gave low one minute Apgar scores more often than did spontaneous vertex delivery in both twins. Full term twins and infants weighing more than 2500g. had fewer low one minute Apgar scores than the preterm infants and those with low birth weight. Perinatal mortality (PNM) in the total series was 14.77% (A 12.50% and B17.05%). The most common cause of perinatal mortality was prematurity in 44.87%. The worst outcome was recorded for the age groups 15-19 and ${geqq}$40, in which perinatal mortality were 50.00%, respectively. The perinatal mortality of both A and B infants was lowest in the group diagnosed early during antenatal care before delivery. On the basis of our findings, we wish to emphasize particularly the importance of the early diagnosis of twins.