This prospective nationwide study conducted during 1982-1985 examined the rates of hypertensive disorders, perinatal mortality and morbidity in 491 insulin-dependent diabetic pregnancies (White's classes: B, 164; C, 129; D, 172; F, 26) and in the total population of 279,000. The rates of pregnancy-induced hypertension (PIH) or pre-eclampsia (20.6%), premature delivery (24.6%), and cesarean section (45.2%) in the diabetic group were more than four times higher than normal. PIH or preeclampsia occurred significantly (p < 0.01) more frequently in patients with diabetic microangiopathy. Mean birthweight was similar in the two populations but gestational age was significantly (p < 0.001) shorter (38 weeks) in the diabetic group. The rate of large for gestational age infants (20%) in the diabetic group was considerably above normal (3.5%). Although perinatal mortality rate in the diabetic group was only 3.1%, it was 4.4 times higher than normal; five of ten fetal deaths were associated with poor glycemic control and thus may not really be unexplained. Neonatal morbidity was significantly more frequent in the diabetic group; still, the incidence of idiopathic respiratory distress syndrome was only 1.6% compared with 0.6% in the general population. Discriminant analysis revealed that gestational age at birth and elevated maternal HbA1c values in early pregnancy independently of each other had a significant impact on the occurrence of neonatal morbidity.