The neonatal survival rate of 500 VLBW (less than or equal to 1 500 g) treated in the neonatal unit of the Departement of Paediatrics in Lausanne (C.H.U.V.) was studied according to changing patterns of nursing and medical care occurring in four successive periods (1961 IX-1963, X-1963 - 1965, 1966-1968, IV-1971-1973). The survival rate at 28 days increased from 35.5% to 47.7% between 1961 and 1965. Earlier start of feeding, intravenous fluid therapy, better control of ambient temperature and better oxygenotherapy are the main changes during this period. Further improvement in neonatal care did not affect the 28-day survival rate. 213 VLBW out of 500 (42.6%) survived at 28 days, 13 (6.1%) out of these died within the first two years of life, 36 (16.9%) were lost for the follow-up. The remaining 164 VLBW were followed until ages between 18 months and 8 years. The improvement in neonatal care was associated with a decrease in the incidence of major neurological sequels from 21.1% to 12.2% between 1961 and 1973. Cerebral palsy and epilepsy are responsible for this decrease. The incidence of mental retardation (DQ or IQ less than 80) also decreased from 17.5% to 4.9% during the same period. However, the incidence of retrolental fibroplasia remained stable. The outlook for VLBW infants is now much more encouraging. Further improvement in perinatal care is likely to further reduce the incidence of major handicaps. but it is not clear whether they will affect the incidence of minor problems such as learning difficulties or poor school performances. More prospective studies are necessary to clarify these points and to ensure early detection of these developmental problems.