GCG and hereditary pheochromocytoma-paraganglioma: The reasons why the present case showed no hypoglycemic symptoms were unclear; however, we can propose some hypotheses for this: pheochromocytoma might reduce hypoglycemia due to insulinoma; at the time of hypoglycemia, our patient overate unconsciously; and glucagon secreted from glucagon-positive tumor cells compensates hypoglycemia.