Gastrinomas are defined as gastrin producing tumors that are associated with an elevated fasting gastrin serum level, a positive gastrin secretin stimulation test and certain clinical symptoms, e.g. recurrent peptic ulcer disease and occasionally diarrhea, the so-called Zollinger-Ellison syndrome. Most gastrinomas occur in the duodenum (approx. 70%) and not in the pancreas. The duodenal gastrinomas are small, and when they occur in association with the genetic syndrome of multiple endocrine neoplasia type 1 (MEN1), they are multicentric and originate from precursor lesions. The prognosis of duodenal gastrinomas is better than that of pancreatic gastrinomas, since despite early lymph node metastasis they progress slowly to liver metastasis.