Abstract： Objective To summarize the diagnosis and therapeutic experience of insulinoma in order to improve the surgical success rate and prognosis. Methods The clinical data of 138 patients with insulinoma from 1966 to 2007 were retrospectively analyzed. Results In this group of patients, hypoglycemia of different levels and Whipple triad were detected. 64 patients expressed different psychic symptom, 12 patients' psychic symptom were still present after blood glucose normalized after operation. Fasting serum insulin values in 88 patients were measured, and the insulin release index was higher than 0. 3. Before operation, tumor was detected in 8 of 75 patients by B-ultrasound scan, and in 17 of 68 patients by CT, and in 5 of 10 patients by MRI. The intra-operative B-ultrasound (IOUS) examination was applied in 44 cases, and 43 cases were successfully detected. The operations included enucleation of insulinoma (n=88) , resection of the body and tail of pancreass (n = 44) , pancreaticoduodenectomy (n=2) , and biopsy (n=1). The blood glucose symptoms normalized postoperatively in 132 patients. The blood glucose rebound in 110 patients, but blood glucose normalized within 2 weeks. After operation, 20 patients developed pancreatic fistula, 32 patients developed acute pancreatitis. Conclusions Insulinoma could be qualitatively diagnosed according to Whipple triad and the insulin release index. Operations with IOUS were simple and effective methods to localize the tumors. The only way to cure insulinoma was operation, and IOUS guided operation could avoid main pancreatic duct and vessel injury, decrease post-operative complications.