A retrospective population study in Northern Ireland examined the benefits of centralized care in insulin-dependent diabetic pregnancies. In the 5 years 1979-1983, there were 139, 250 deliveries in Northern Ireland and of these 221 pregnancies occurred in 187 insulin-dependent diabetic patients; 100 were managed entirely in peripheral maternity units, 61 were referred from a peripheral unit to the Royal Maternity Hospital, Belfast and 60 were managed entirely in this central referral hospital. The patients referred from the periphery had the worst past obstetric history with a combined perinatal mortality rate of 200 per 1000. During the study period the perinatal mortality rate was 107 for the referred pregnancies, 33 for those managed entirely in the peripheral units and 18 for those managed at the Royal Maternity Hospital. If those pregnancies terminated for fetal abnormality, and deaths beyond the perinatal period are included, the figures for total fetal loss were 15.5%, 5.5% and 7.1% respectively. Overall the major congenital malformation rate was 7.5%, and for the respective groups 6.5%, 3.0% and 13.0%. For the general population during the same period the perinatal mortality rate was 1.4% and the major congenital malformation rate was 2.5%. Thus it is suggested that only peripheral hospitals which can offer combined antenatal/endocrine care and with a neonatal intensive care unit should undertake the management of the pregnant diabetic.