Transient neonatal diabetes mellitus is an uncommon disorder. Macroglossia in association with transient neonatal diabetes mellitus has been reported only twice before. We report the case of a 21-day-old male infant referred from a peripheral hospital for management of hyperglycemia. The mother was a 21-year-old primigravid in good health. There was no history of diabetes or drug or alcohol exposure. The pregnancy was complicated by intrauterine growth retardation and oligohydramnios from 30 weeks' gestation and the birth weight at 38 weeks' gestation was only 1480 gm. Physical examination revealed dysmorphic features and asymmetric growth retardation. The admission weight (1840 gm) and length (40.5 cm) were 5 SDs less than the mean and head circumference (32.5 cm) was 1 SD less than the mean. Dysmorphic features included macroglossia, large fontanelles, hypospadias, umbilical hernia, and bilateral inguinal hernias. Hyperglycemia had been noted on day 1 of life with an initial blood glucose value of 16 mmol/L (288 mg/dl). Despite treatment with regular insulin blood glucose control continued to be erratic. Therefore a regimen of daily NPH insulin was begun, which has a smoother action. Interestingly, from day 41 to day 47 the infant did not receive insulin and a crude control of the blood glucose was demonstrated. Peak levels of blood glucose in excess of 20 mmol/L (360 mg/dl) were followed by drops to levels less than 2 mmol/L (36 mg/dl) without insulin administration. This abnormal pattern of glucose control may represent poorly regulated release of endogenous insulin. However, because of unsatisfactory glucose levels administration of daily NPH insulin was reintroduced. The infant was discharged from the hospital on day 50 and administration of insulin was discontinued uneventfully at 9 months. At 1 year the hemoglobin A1c level was still normal and the infant's weight was at the 10th percentile. Macroglossia was less pronounced. Development showed mild delay in gross motor milestones.