A 62-year-old man admitted to our outpatient clinic with two months of recurrent life threatening hypoglycemia episodes. He was diagnosed as malignant insulinoma with multiple metastases of liver and peripancreatic lymph nodes. Liver biopsy specimen was demonstrated grade 2 neuroendocrine tumor compatible with clinical and radiological results. He was followed under the treatment of continuous intravenous glucose infusion during the diagnostic procedures. He had a pancreatic lesion history measured 20 x 12 mm in diameter via the abdominal tomography examination approximately two years before the diagnosis. Unusual course of this case suggests the transformation of nonfunctioning pancreatic neuroendocrine tumor into functional insulin secreting tumor with metastases. The patient was found inoperable and started on chemotherapy.