Herein, we report two cases of pancreatic nesidiodysplasia, an extremely rare cause of hyperinsulinemic hypoglycemia in adults. The first case was a 43-year-old, nonobese female with recurrent hypoglycemia after 10% distal pancreatectomy with splenectomy performed 16 years previously for insulinoma. Three suspect tumors were found on the preoperative angiograms and second operation, but the pathologic finding revealed diffusely scattered microscopic nodules with a background of nesidiodysplasia. The second case was a 52-year-old female with a five-year history of hypoglycemia. Extensive diagnostic procedures revealed a suspect insulinoma over the pancreatic body. The histology confirmed diffuse nesidiodysplasia. Both cases were diagnosed as insulinoma before surgical intervention because of the hypoglycemic symptoms, high insulin/glucose ratio and the positive image studies. The pathologic findings were characterized by the budding of islet cells from the pancreatic duct epithelium with diffuse islet hyperplasia. Both patients remained well after 75% to 80% pancreatectomy with no recurrence of hypoglycemia. The etiology, pathology, preoperative work-up, and operative strategy of nesidiodysplasia are discussed.