In a retrospective analysis of perinatal influencing factors in 186 premature newborns of the Department of Gynaecology of the University of Erlangen covering the period from 1982-1987 with birth weights between 500 and 1500 grams, the mortality and early morbidity were analysed, as characterised by cerebral haemorrhages, respiratory distress syndrome and infections insofar, as they had been connected with the obstetrical approach and paediatric intensive-care treatment, 45 infants born in 1982/83 were compared with 141 infants, who had been subjected to a different treatment approach during 1984 to 1987. During the second period, there was a marked drop both in mortality and in the incidence of asphyxia-induced severe cerebral haemorrhage and of the respiratory distress syndrome. A shortened latency period after premature rupture of the amnion, and a more pronounced presence of a neonatologically experienced team of paediatricians were found to be significant obstetric liberal influencing factors in determining the need to perform Caesarean section. The triplication of the frequency of Caesarean section observed resulted in a 50% reduction in perinatal mortality and morbidity. Infants with pelvic presentation benefited most from the more liberal performance of Caesarean section, as did infants with vertex presentation. Shortening of the latency phase in premature rupture resulted in a marked reduction in infection morbidity and mortality. Therefore we conclude, that the frequently practised procrastination with the aim to await an improvement in lung maturity should be replaced by a more active obstetric management, avoiding both infection and birth trauma. Obstetric decisions should be based rather on prenatal estimation of weight than on the calculated gestational age. At present, the lowest birth weight associated with the expectation of a healthy life is considered to be 750 grams.