A clinical investigation was undertaken to challenge the commonly accepted view that the interval between the birth of the first and second twins should be preferably within 15 minutes and certainly no more than 30 minutes. During 1981 and 1982, 115 patients with live-born twins at 34 or more weeks' gestation underwent an attempted vaginal delivery at four regional perinatal centers. The interval between vaginal delivery of the first and second twins (mean, 21 minutes, range, one to 134 minutes) was 15 minutes or less in 70 (61%) cases and more than 15 minutes in 45 (39%) cases. Excluding conditions associated primarily with prematurity, all second twins delivered beyond 15 minutes did well despite the delay and had no signs of excess trauma or low five-minute Apgar scores. Maternal complications were also uncommon, although combined vaginal-abdominal delivery was more frequent if there was a delay of more than 15 minutes (eight of 45 versus two of 70, P less than .02). The authors conclude that if there is continuous fetal and uterine monitoring, a time restriction for the delivery interval between the first and second infants is not necessary.