The results of management of 128 consecutive pregnancies occuring in diabetic patients who received insulin from before conception and throughout pregnancy are described. Mean maternal blood glucose levels were at least 1 mmol/litre greater than levels reported in normal pregnancy. Thirty-nine percent of the neonates had significant morbidity; respiratory distress syndrome (7·7%), hypocalcaemia (4·6%) and polycythaemia (10%) could be related to higher maternal blood glucose levels. Neonatal hypoglycaemia (9·2%), hyperbilirubinaemia (13·8%) and birth weight corrected for gestational age were not directly related to maternal blood glucose. This degree of maternal blood glucose control has reduced the large for dates infants (greater than 90th centile for gestational age) to 7%. Further reduction in the morbidity of infants of diabetic mothers requires studies of physiological maternal blood glucose levels which may not be possible with conventional insulin treatment as well as further efforts to reduce prematurity.