More than 90% of insulinomas are benign tumors. Insulinomas cause hypoglycemia and thereby symptoms of neuroglycopenia and catecholamine response. During symptoms, blood glucose levels should be less than 40 mg/dl (less than 2.2 mmol/l), concomitant insulin levels should be ≧6 IU/ml (≧43 pmol/l) and concomitant C-peptide levels ≧0.2 pmol/l. Most insulinomas can be identified intraoperatively by experienced surgeons. Initial therapy consists of administration of frequent meals and/or by glucose infusion. In patients with solitary insulinomas, complete surgical removal of the tumor should be the primary goal. In patients with metastatic insulinomas, symptoms of insulin hypersecretion will only completely disappear after complete resection of all metastases.