Data from 634 newborn babies with birthweights less than or equal to 2000 g admitted to the South West Thames Regional Neonatal Unit in St George's Hospital since its opening in 1980 were analysed. Only 271 (43%) of the pregnancies were booked there; 200 (32%) of the babies were transferred in utero and 162 (26%) after delivery. Weight-specific neonatal survival rates, calculated after exclusion of lethal abnormalities showed that between 1001 and 1500 g, 79 (96%) of the 82 babies transferred in utero survived in 1981-1984, compared with only 57 (79%) of the 72 postnatal transfers (P less than 0.02). Under 1000 g, no such differences were found, possibly because paediatricians transferred only the fitter babies in this weight range. The birth of very-low-birthweight babies of short gestation in units unable to provide immediate resuscitation, adequate stabilization and full neonatal intensive care is a major risk factor for increased neonatal mortality. These findings support the role of regional perinatal centres as service units for antenatal transfer and neonatal intensive care, and as teaching centres.