ABSTRACT.Three hundred and seventy‐seven consecutive liveborn infants with a birthweight between 500g and 1500g born at two perinatal centres in the calendar years 1977 and 1978 and 40 outborn infants in the same weight group admitted to one of the hospitals during the same period were studied. Although the survival rates in individual 100g weight groups vary between 14.3% and 97.4%, overall survival rates for inborn and outborn infants in both hospitals were similar, ranging from 69.0% to 71.5%. Twenty‐two perinatal factors were found to have a significant effect on survival, of which 15 were common to the inborn populations in both hospitals. Eight of these 22 factors were indicators of intrapartum asphyxia. Multiple regression analysis showed that whereas birthweight was the most important variable influencing outcome in one hospital, the infant's condition at birth is the most important in the other. This difference may be related to the aggressive approach to perinatal intensive care of extremely preterm infants in the latter hospi