Insulinomas are the most common functioning endocrine tumors of pancreas. Approximately 10% are multiple, less than 10% can be malignant and 5-10% associated with the MEN-1 syndrome. Insulinomas are the most common cause of hypoglycemia resulting from endogenous hyperinsulinism. The aim of this lecture is to present the up-to-date information concerning the prevalence, diagnosis and treatment of insulinoma.