During a period of 13.5 years 17 patients with a gastrinoma and an associated Zollinger-Ellison syndrome were treated. In three patients (18%) the gastrinoma was part of a multiple endocrine neoplasia type I (MEN I). The median interval from the initial symptoms to the definite diagnosis was 5.0 years. During this interval seven patients (41%) underwent gastric surgery up to four times. The preoperative imaging studies localized the primary tumor in only seven patients (41%). In five of six diagnostic laparotomies the primary site of the tumor was identified and proved by pathologic work-up. The surgical procedures (n = 13) included five resections of the pancreas (3 x pancreatic head, 2 x left pancreatic resection), two duodenal resections, three enucleations of the tumor and three palliative operations (hospital mortality: 0%). Following laparotomy the gastrinoma could be histologically proved in eleven of 17 patients (6 x pancreas, 4 x duodenum, 1 x in the hepatoduodenal ligament). The rate of metastatic spread as characteristic feature of malignancy was 59%. After complete resection of the primary tumor (n = 8) none of these patients died because of the gastrinoma during the follow-up (median: 7.3 years). In the remaining patients three deaths were caused by the metastatic spread of the gastrinoma. Considering the high rate of preceding operations, the high malignancy rate and the excellent prognosis after RO-resection the diagnostic interval in patients with ZES is too long. Despite the modern radiographic imaging the exploratory laparotomy is of high value in patients with ZES.