We recently observed a pancreatic islet cell adenoma with nesidioblastosis in a neonate which was confirmed after subtotal pancreatectomy. A nesidioblastosis, a term coined by Laidlaw in 1938 to describe the neoformation of islet tissue by differentiation of tortipotent pancreatic duct cell, is extremely rare as a cause of neonatal hypoglycemia. Persistent hypoglycemia which was temporarily responsive to hypertonic glucose therapy, convulsion, and apnea were noted frequently. Blood insulin level was elevated inappropriately with respect to the blood glucose level. Preoperative CBC, urinslysis, chest X-ray, serum electrolytes, and ECG were normal except low blood glucose leve(21mg%). The patient was not permedicated. With infusion of 15% D/W, anesthesia was induced by tracheal intubation with 3mg/kg of succinylcholine and was maintained by controlled ventilation with O2(3L/min)-N2O(3L/min)-halothane(1%) and pancuronium. Hyperglycemia and hypoinsulinemia were developed after pancreatectomy, these were controlled satisfactorily by administration of regular insulin. The patient was discharged with normal blood glucose level and no requirement of insulin at 38 days of postoperation.