INS and pancreatic insulinoma: Although hypoglycemia was recognized as early as the 19th century, hyperinsulinism was suspected to be the cause of hypoglycemia in nondiabetic patients.1 The first case of a pancreatic islet cell tumor was described by Nicholls in 1902,2 but the possibility of an insulinoma was not appreciated until 5 years after the discovery of insulin in 1922.