In a consecutive series of 600 pregnancies (618 infants) in 300 clinically diabetic patients, the maternal mortality was 0 and the loss of viable infants was 9.5%. Therapeutic abortion and sterilization were not practiced. The cesarean section rate was 23%. The major causes of perinatal loss were hyaline membrane disease and congenital malformations. Recent routine estimation of the L/S [lecithin/sphingomyelin] ratio in amniotic fluid led to a reduced incidence of respiratory distress syndrome and a consequent improvement in perinatal mortality. Strict control of diabetes is essential.