A large, one-hour-old female baby was noted to have hypoglycemia immediately after birth. Although early feeding and then intravenous glucose infusion with a dose gradually increased to 30 mg/kg/min were given, the baby still had recurrent hypoglycemia 14 days after birth. High serum insulin/glucose ratios (> 2.5) were noted twice during hypoglycemic episodes. At the same time, the baby's serum growth hormone, thyroid hormone and cortisol levels were within normal ranges. Hyperinsulinism due to nesidiodysplasia was diagnosed and a near-total pancreatectomy was performed at the age of 14 days. After the operation, euglycemia was achieved and there was no episode of hypoglycemia even after fasting for eight hours. Our experience confirms that surgery is the treatment of choice for patients, including neonates, with hyperinsulinemic hypoglycemia.