Persistent hypoglycemia in the neonate is rare and may be due to inborn errors of carbohydrate metabolism, islet cell tumors, or unknown causes. A patient with the onset of symptomaric hypoglycemia at 36 hours of age had persistent hypoglycemia in spite of therapy with corticosteroids, A.C.T.H., Diazoxide, glucagon, parenteral glucose and fructose. She showed a normal hyperglycemic response to glucagon. Plasma insulin values were not diagnostic. At surgery, at 7 weeks of age, a discrete islet cell adenoma was found and removed with the body and tail of the pancreas. The spleen was not removed. Following surgery, she had a transient hyperglycemia and required insulin for 8 days with a wound infection. She has remained normoglycemic.