PURPOSE: The diagnosis and treatment of insulinoma are very important because the tumor can induce critical and permanent neurological deficit. The purpose of this study was to gain an understanding of the clinical features of insulinomas and to establish the diagnostic and therapeutic strategies. METHODS: 17 patients, preoperatively diagnosed with insulinomas and who had undergone surgical management between January, 1998 and March 2004, at the Department of Surgery, Samsung Medical Center, were analyzed. RESULTS: After the operation the 17 patients were diagnosed pathologically; 13 insulinoma, 2 nesidioblastosis, 1 endocrine tumor and 1 endocrine carcinoma. The male to female ratio was 7: 10, with a mean age of 52.3 years. All the patients had symptoms of Whipple triad. The mean duration of symptoms to surgery was 18 months. The preoperative mean blood sugar, plasma insulin, C-peptide and insulin to glucose ratio were 39.6 mg/dl, 47.4muU/ml, 4.8 ng/ml and 1.02 respectively. Preoperative localization was achieved in 15 patients by combining ultrasonography, angiography, abdominal CT and intra-arterial calcium stimulated venous sampling and sensitivity of those examinations were 60, 61.5, 73.3 and 91.7%, respectively. Intraoperative localization was also performed by a combination of manual palpation and intraoperative ultrasonography in 15 patients, with retrospective sensitivities of 86.6 and 100% respectively. The frequenies of head, body and tail were 6: 3: 6. In 2 nesidioblastosis patients, the localization failed both pre- and intraperatively. The types of operations included 11 enucleations, 3 distal pancreatectomies, 2 blind subtotal pancreatectomies and a distal pancreatectomy combined with an extended left hemihepatectomy and intraoperative radiofrequency ablation (RFA) for one patient accompanied by multiple liver metastase. 13 insulinomas were benign, small (mean diameter 1.5 cm, maximum 2.3 cm) and solitary, with the exception of one patient with MEN I. The symptoms of hypoglycemia and the laboratory values were improved in all patients after the operation. CONCLUSION: Insulinomas may be readily localized using sensitive diagnostic tools, such as intra-arterial stimulated venous sampling or intraoperative ultrasonography with manual palpation. If possible, enucleation may be a curative and feasible procedure for benign insulinomas. However, in the case of a highly suspicious nesidioblastosis, a blind partial pancreatectomy may be used as a trail method.