Islet cell neoplasia is a frequent occurrence in multiple endocrine neoplasia type 1 (MEN 1). Sixteen of 27 patients with MEN 1 developed functioning endocrine pancreatic tumor syndromes. Eleven of the 16 developed Zollinger-Ellison syndrome and each was evaluated by a combination of computed tomography and hepatic angiography to exclude hepatic metastasis and percutaneous transhepatic catheterization to localize the tumor. Seven of the 11 patients were found to have duodenal gastrinomas with multiple duodenal tumors in three patients. Four of the 11 patients had only pancreatic gastrinomas. In addition to the gastrinomas, other types of islet tumors in the pancreatic body or tail were found in nine of the 11 patients. None of the patients had hepatic metastases. Seven of the 11 patients were treated by distal pancreatectomy and since 1986 all patients have had duodenotomies as part of the surgical exploration. Postsurgical evaluation ranging from three months to 14 years indicates that 10 of 11 patients have normal basal gastrin levels. We conclude that duodenal gastrinomas are common in MEN 1 and can be managed successfully by appropriate operative intervention.