PURPOSE: Insulinomas are a rare disease, which can be cured by surgical management if diagnosed early. However, diagnosis and localization are difficult, due to their small size and varied clinical manifestations. We analyzed the clinicopathological features, diagnosis and surgical management of insulinomas. METHODS: We retrospectively analyzed 12 insulinoma patients who had undergone pancreatic surgery, between 1988 and 2001, at the Department of Surgery, College of Medicine, The Catholic University of Korea. RESULTS: The male to female ratio of the insulinoma patients was 1: 1 with a mean age of 37.9 years, ranging from 20 to 65. The clinical manifestations were loss of consciousness, weakness, confusion and dizziness, and all the patients had findings compatible with Whipple's triad. The median duration of symptoms before surgery was 16.8 months, ranging from 1 to 48 months. Hyperinsulinemic hypoglycemia was confirmed, during prolonged fasting, when the concomitant fasting blood sugar level was 42.4mg/dl and insulin level was 25.2 microU/ml (8.1~61.8 microU/ml). The insulinoma can be localized in 11 patients (91.7%) preoperatively. For the preoperative localization, a transhepatic portal vein sample (THPVS), selective angiography and a CT scan were good diagnostic methods. Intraoperative ultrasonography was the most useful localization tool during the operation. For treating the insulinoma, an enucleation, a distal pancreatectomy, and a pylorus preserving pancreaticoduodenectomy were performed in 5, 6 and 1 patients, respectively. An enucleation case was diagnosed as nesidioblastosis after surgery, thus needing a near total pancreatectomy. One patient with a multiple endocrine neoplasia (MEN), subtype I, needed a thyroidectomy and an adrenalectomy. All cases were single, benign tumors within the pancreas. The symptoms of hypoglycemia and the laboratory values were normal in all patients after surgery. CONCLUSION: We experienced 12 insulinoma patients, where preoperative suspicions, proper utilization of diagnostic tools, and prudent intraoperative diagnostic procedures enhanced the diagnostic accuracy of the insulinoma, and led to better treatment strategies.