Duodenal carcinoid tumors are uncommon. It is not known whether they behave more like carcinoid tumors in the appendix (indolent course) or those in the ileum (often virulent)-crucial information for determining the need for radical resection. A retrospective review at our tertiary referral center (from 1976 to 1999) identified 27 patients with primary duodenal carcinoid lesions, excluding functional islet cell tumors. Endoscopic biopsy provided the diagnosis in 78% of patients. Treatment was by endoscopic excision (n = 11), transduodenal excision (n = 8), pancreaticoduodenectomy (n = 3), segmental distal duodenectomy (n = 2), or palliative operation (n = 2). One patient did not undergo operation because of comorbidity. Eighteen of 19 patients with tumors smaller than 2 cm remained disease free after local (endoscopic or transduodenal) excision. The exception was a patient with a small periampullary carcinoid lesion. In contrast, all four patients with carcinoid tumors 2 cm or larger who were resected for cure developed a recurrence (2 to 9 years postoperatively). We conclude that duodenal carcinoid tumors smaller than 2 cm may be excised locally; to ensure complete resection we recommend open transduodenal excision for tumors between 1 and 2 cm. Endoscopic follow-up is indicated. It is unclear whether patients with larger tumors benefit from more aggressive locoregional resection. Ampullary/periampullary carcinoid tumors should be considered separately, as their behavior is unpredictable.