There have been new developments in the diagnosis and therapy of Zollinger-Ellison syndrome. The main symptoms of the syndrome are ulcers at atypical sites and nocturnal hypersecretion. Diarrhea and steathorrhea are equally common and may be misinterpreted. Diagnosis is established by the paradoxical rise in plasma gastrin after intravenous secretin provocation. Fasting plasma gastrin levels alone may be misleading and suffer from both false positive and false negative results. Previously, total gastrectomy was necessary to prevent complications. Today the symptoms can be controlled by adequate H2-receptor blocker treatment, if necessary combined with an antimuscarinic drug such as pirenzepine. Exploratory surgical attempts to remove the tumor have a success rate of only 20% and only half of those may be cured. However, the new technique of transhepatic pancreatic vein catheterization, supplemented by determination of local hormone gradients, allows preoperative localization of even small tumors. In the last two years the author has had experience of 5 patients with endocrine tumors of the pancreas (1 insulinoma, 4 gastrinoma) who underwent this procedure. In every case the tumor was localized, removed by surgery and the patients subsequently cured of the syndrome, even including 2 patients with multiple endocrine neoplasia (MEN 1). It is concluded that this chance of cure should be offered to every patient with this syndrome.