A 45-year-old woman was referred to us for hypoglycemia. The patient had been operated on for a duodenal ulcer by bilateral troncular vagotomy and pyloroplasty 20 years ago and, since then, she showed a dumping syndrome. Two months before consultation she developed repetitive episodes of symptomatic hypoglycemia. An oral glucose tolerance test showed hypoglycemia with endogenous hyperinsulinism. The continuous glucose monitoring system sensor demonstrated fasting hypoglycemia. The endoscopic ultrasound of the pancreas showed a pancreatic tumor that was confirmed in the pathologic study after surgery. Moreover, nesidiodysplasia image was found surrounding pancreatic parenchyma. We report, for the first time, both histologic lesions associated in a patient with a history of vagotomy and pyloroplasty for a duodenal ulcer and we discuss the possible pathogenic mechanisms.