Of 75 patients with neuroendocrine tumors of the gut, 50 had functioning lesions, causing endocrine syndromes. These included 16 insulinomas, 13 gastrinomas, 5 vipomas (4 pancreatic, 1 adrenal), 4 corticotrophinomas, and 1 renal enteroglucagonoma. Three patients had mixed endocrine syndromes. Eight or 9 patients with pancreatic lesions had multiple endocrine adenopathy (MEA I), including 3 of 4 patients with multiple insulinomas and all 3 patients with malignant gastrinomas. Localization of the pancreatic insulinomas, vipomas, and mixed tumors by arteriography was excellent, but few gastrinomas were detected before operation. Eight patients developed the malignant carcinoid syndrome with metastases from primary tumors in the ileum (6 patients), bronchus, and stomach. Hepatic artery embolization provided palliative relief for several with this and some other syndromes. Twenty‐five patients had tumors that caused nonspecific features only. These included 18 appendicular carcinoids, 5 islet cell carcinomas, and 2 other apudomas (1 hepatic and 1 whose primary site is unknown). The importance of the latter is that they are more responsive to therapy and have a better prognosis than the more common acinar tumors. Over 40% of the patients had lesions that were cured surgically and over 80% obtained some benefit from treatment.