The centralisation of high risk deliveries in perinatal centres has become standard practice in most developed countries over the last 20 years. The goal of this study was to assess to which extent this practice has been implemented in Switzerland as well. In addition, we compared standard morbidity outcome measurements between outborn and inborn infants, as well as the frequencies of postnatal interhospital transfers. METHODS: All infants born alive either below the 32nd week of gestation, weighing less than 1500 g, or who required assisted ventilation before the 44th week of corrected gestational age were entered in a prospective epidemiological survey (Swiss minimal neonatal data set) if they had been admitted to a neonatal intensive or intermediate care unit. We analysed the data derived from infants born between 1 January and 31 December 1996. RESULTS: 86% of the 720 infants of less than 32 weeks gestation and/or less than 1500 g (group 1) were born in a perinatal centre, whereas only 27% of the 508 infants > or = 32 weeks gestation and > or = 1500 g who required assisted ventilation (group 2) were inborn. In group 1 outborn infants had a higher risk for pulmonary hypertension (odds ratio 3.7, 95% confidence interval 1.4 to 10.0), for hyperechogenic leucomalacia (odds ratio 2.7, CI 1.3-5.4), for necrotising enterocolitis (odds ratio 2.5, CI 1.1-5.7). The frequencies of postnatal interhospital transfer were the following for group 1 and 2: once 35% vs. 52%, twice or more 10% vs. 31%. CONCLUSION: 720 infants below 32 weeks gestation and/or < 1500 g were admitted to neonatal units in 1996 which corresponds to 0.86% of all liveborn infants in Switzerland. Fourteen percent of these infants were outborn with a high morbidity. Of the 508 larger and older new-born infants who required assisted ventilation (0.62% of all liveborn infants in Switzerland), 73% were outborn. It is speculated that improved prenatal identification of risk factors and prenatal transfer could further reduce the morbidity of these two populations of new-born infants.