On the basis of data from the Medical Birth Registry of Norway the authors have analysed the births that occurred during transport to hospital in Norway during the period 1967-88. They conclude that such deliveries have increased, but their excess perinatal mortality has been eliminated. Thus the proportion of infants born during transportation increased from 1.6 per 1,000 births in 1967 to 2.5 in 1988 when 145 infants were born on the way to hospital. The increase in such births was greatest in remote municipalities. This had been anticipated, due to the closing down of a large number of small hospitals. On the other hand, there were fewer such births among mothers with high risk of perinatal health problems, such as nulliparae, among unmarried mothers and mothers with specified diseases in pregnancy and also for infants with low birth weight. During the period 1967-70, perinatal mortality was seven times higher among infants born on the way to hospital. Perinatal mortality declined rapidly during the late 1970s and towards the end of the observation was nearly the same as for all other infants. This indicates that the adverse effects of centralization have to a large extent been avoided.