Preexisting type-I-diabetes (incidence 0.8%) and gestational diabetes (3-5%) are the two manifestations of disturbed carbohydrate metabolism in pregnancy. Maternal hyperglycemia and the resulting excessive glucose supply for the fetus leads to fetal hyperinsulinism which is responsible for the complications in the offspring. The most important clinical manifestations are the excessive growth of the fetus (macrosomia), the risk of intrauterine death and the neonatal morbidity caused by hypoglycemia and the delay of maturation of lungs and liver. Women with type-I-diabetes require preconception counseling and optimizing of glucose control to reduce the rate of abortion and of congenital anomalies of the offspring. Furthermore kidney function and retinopathia should be evaluated preconceptionally. The management of diabetic pregnancies requires a tight cooperation of obstetricians and diabetologists. Blood glucose levels have to be lower than outside pregnancy. Gestational diabetes is diagnosed by a screening test with 50 g glucose for all women followed by a regular 75 g oGTT when the glucose value is > or = 140 mg%. In most of the women euglycemia can be achieved by diet and exercise. Women after pregnancies with gestational diabetes should be retested postnatally and counseled about their increased risk to develop diabetes in later life.