The incidence of insulinoma, an insulin-producing tumour arising from pancreatic beta-cells and responsible for the development of fasting hypoglycemia, in the general population is 1-4 per 1,000,000 yearly, mostly at the age of 25-55 yr. Malignization of this neoplasm occurs in 10-15% of the cases. One third of the tumours produce metastases. The most characteristic clinical manifestation of insulinoma is the Whipple's triad, with episodes of fasting hypoglycemia (below 2.8 mmol/l) correctable by intravenous glucose injection or intake of sugar. The authors report a case of intravital diagnosis of malignant metastasizing insulinoma in a 82 year old woman with type 2 diabetes mellitus. A review of relevant literature is presented.