Insulin-secreting tumors are the commonest hormone-producing neoplasm of the gastrointestinal tract. They occur with an incidence of 4 cases per million per year. About 10% of them are metastatic and malignant insulinomas very rarely observed in children and in elderly. We report a rare case of very large malignant insulinoma in a 71-year-old woman admitted in our Oncological Institute on October 2005. She presented with fasting hypoglicemia (blood glucose 35 mg/dl) and high serum insulin levels (insulin 115.9 microU/ml). A computerized tomographic scan showed a pancreatic tail lesion of about 6 cm in max diameter and multiple liver metastases. A whole body scintiscan using 111In-DTPA-D-Phe1-octreotide was made and an increased uptake in the tail of the pancreas has been found. The patient was submitted to liver biopsy and the diagnosis of a metastatic insulin-secreting tumor was immunoistochemically confirmed. Due to the presence of some hypoglicemic episodes uncontrolled by medical treatment, on December 2005 the patient was admitted to surgical intervention with a body and tail pancreatic resection. Post-operatively the patient experienced again syncope with hypoglycemia and hyperinsulinemia. It was then decided to start a schedule of treatment with somatostatin analog (octreotide subcutaneously 500 microg three times a day) with a good control of blood glucose levels (101 mg/dl). A trans-arterial chemioembolization was planned but the patient died for pancreatic and cardiovascular complications before this treatment started.