Seventy-three patients with overt diabetes were followed during pregnancy with tight control of carbohydrate metabolism and frequent measurement of glucose levels. During the last 12 weeks of pregnancy, mean plasma glucose levels averaged 108 mg/dl. Mean fasting plasma glucose levels averaged 98 mg/dl. Of the 73 patients, 77 per cent had mean plasma glucose levels of less than 120 mg/dl. Perinatal mortality rate was 4 per cent; this was corrected to 1.4 per cent when congenital anomalies incompatible with life were removed from consideration. Patients were allowed to go as close to term as possible, with 51 per cent being delivered at or beyond 38 weeks. Only two babies (2.8 per cent) were delivered because of deterioration of fetoplacental function test results. The results of this suggest that tight metabolic control may prevent some of the fetal morbidity associated with overt diabetes in pregnancy.