Insulinomas are rare tumors whose difficult diagnosis is usually delayed with respect to appearance of the first symptoms. The Whipple triad (symptoms of hypoglycemia, low blood glucose and rapid alleviation of symptoms after glucose administration) associated with an increase in plasma immunoreactive insulin (IRI) and low blood glucose levels constitute the diagnostic basis of insulinoma as the cause of organic hypoglycemia. Curative treatment entails surgery and its success will depend on the location of the tumor. Selective arteriography and, more recently, percutaneous transhepatic insulin determination (IRI) in the splenoportal axis have a diagnostic rate of 90%. Nevertheless, none of these topographic diagnostic methods replaces meticulous intraoperative exploration of the pancreas, which in our case was definitive for cure.