An insulinoma is a tumor of the pancreas derived from the beta cells which while retaining the ability to synthesise and secrete insulin is autonomous of the normal feedback mechanisms. Patients present with symptomatic hypoglycaemia which is ameliorated by feeding. The diagnosis of an insulinoma is usually made biochemically with elevated insulin, proinsulin and C-peptide levels and confirmed by medical imaging or angiography. The definitive treatment is surgery.