Hypoglycaemia in birth-asphyxiated and small-for-dates infants is commonly attributed to glycogen depletion. However, 3 infants with asphyxia at birth and 3 small-for-dates infants had unequivocal hyperinsulinism. This suggests that hyperinsulinism may contribute to hypoglycaemia in small-for-dates and asphyxiated neonates.