With the rapid advances in perinatal intensive care and resultant changes in neonatal prognosis, it is often difficult for the medical personnel involved to know where application of such care is justified, whether major intervention for fetal reasons is warranted, or what information to give parents as to probable outcome. To aid in developing guidelines for these areas of concerns, 730 consecutive live births that occurred in a perinatal unit between 23 and 32 weeks' gestation were analyzed for mortality and long-term morbidity by gestational age at birth. Probability of a normal outcome varies considerably according to which method of analyzing outcome is used. With a greater than 50% probability of intact survival from 25 weeks' gestation and above, intervention for fetal reasons seems to be justified if indicated on purely medical grounds, although prolonged use of restricted resources at or below 25 weeks remains a concern.