Here we will discuss two pathologic conditions were GLP-1 has been associated with hypoglycemia, in congenital hyperinsulinism due to inactivating mutations in the KATP channels and in postprandial hypoglycemia after gastrointestinal surgery, where the delivery of nutrients to the small intestine is altered resulting in both hyperglycemia and an exaggerated secretion of GLP-1. The gene discussed is GLP1R; the disease is hyperinsulinism.