To make a diagnosis of insulinoma, one must consider it. Neuroglycopenic symptoms are the most prominent and convincing, and the combination of hypoglycemia and endogenous hyperinsulinemia are diagnostic of insulinoma. A glucose level of approximately 40 mg/dL with a concomitant insulin level of 6 microU/mL, a C-peptide level exceeding 200 pmol/L, and a negative screening for sulfonylurea must be documented to confirm the diagnosis. Although in the author's experience, preoperative ultrasound is the best and often the only test performed in the patient undergoing a first-time operation, arteriography is perhaps the single most effective localization test performed on a nationwide basis. Expertly performed intraoperative ultrasonography assists in tumor localization and in delineating important related anatomy and has become virtually routine in the author's surgical practice. Insulinomas are typically benign, single, and small, and are generally firmer than surrounding normal pancreas. Extensive surgical exposure may be required to identify and safely remove the tumor. Enucleation is preferred by the author, but distal pancreatectomy for tumors in the body or tail is an excellent method as well. Tumors in the head of the pancreas are usually enucleated, and pancreatoduodenectomy is rarely performed. The most troublesome complication is a pancreatic leakage causing pseudocyst, abscess, or fistula. Except in MEN 1 syndrome, in which a more extensive resection is usually indicated, excision of a single benign insulinoma leads to long-term cure of the disease. The successful excision of an insulinoma will profoundly affect a patient's life.