Hypoglycemia is not only significantly reduces the quality of life of patients, but also refers to life-threatening conditions. When clinical and laboratory signs of hypoglycemia appear, regardless of the presence or absence of carbohydrate disorders, it is necessary to clarify the etiology of its appearance. One of the causes of spontaneous hypoglycemia, which occurs principally with fasting, is insulinoma – neuroendocrine tumor, deriving from β-cells of islets of Langerhans, that uncontrollably secreting insulin, approximately 5-10% of them are malignant. The classic diagnostic method is prolonged supervised fasting test (up to 72-hour), during which the classic hallmark – the Whipple triad has been confirmed. Currently, there are a lot of imaging modalities, including scintigraphy, positronemission tomography/computed tomography and invasive imaging studies. Even when the tumor has not been located preoperatively, surgical cure should be performed if the diagnosis of insulinoma has been established biochemically. The somatostatin analogs of short and long-acting have been reported to control symptoms of malignant insulinomas. Interferon-Alfa Therapy and chemotherapy are used as pathogenetic therapy. Even when metastases to the liver are found, cytoreductive surgery (radiofrequency ablation, embolization and chemoembolization of the hepatic arteries) may be perfomed. Research use of the peptide receptor-targeted radiotherapy is underwaying.