The neonatal morbidity and mortality rate of 335 twin pairs born during the years 1965-1973 was investigated. 649 twins were born alive. 29 % of the twins were preterm. 31 % of the twins were small for date infants, and 41% weighed less than 2 500 g. Mean birth weight was 2 590 g in A twins and 2 560 g in B twins. The neonatal mortality (0- 28 days) was 7.1%. The most common causes of death were the respiratory distress syndrome, intracranial haemorrhage and anoxia. Low one minute Apgar scores occurred more often in B twins than among A twins. Breech delivery gave low one minute Apgar scores more often than did spontaneous vertex delivery in both twins. Full term twins and infants weighing more than 2 500 g had fewer low one minute Apgar scores than the preterm infants and those with low birth weight. Neonatal disorders were equally common in both twins except the birth asphyxia and/or aspiration syndrome, which were more frequent in the B twins. The respiratory distress syndrome was diagnosed in 8 % of A twins and 12% of B twins. Hypoglycaemia was recorded for 8%, and hyperbilirubinaemia exceeding 15 mg% for 7 %. Infections occurred in 6%. Transfusion syndrome was verified in 7% and malformations in 6%. Although mortality in twin pregnancies has declined, neonatal morbidity is very high. Twin pregnancies thus form a high risk group for obstetricians and pediatricians.