BACKGROUND We studied the CT patterns of abdominal carcinoid tumors. METHODS Eight patients with carcinoid tumors were examined with CT. The tumors were in the ileum (2 patients), duodenum (1), colon (1), and mesentery (4). Pathologic confirmation was obtained at surgery in all patients. The symptoms were the carcinoid syndrome in 2 patients, abdominal pain in 4, jaundice in 1 patient and a right lower quadrant mass in 1. All patients were examined with(out) i.v. contrast agent administration; 6 patients received oral contrast material and 2 were submitted to water enema, to enhance visualization of the distal ileum and colon. RESULTS CT identified the tumor in all patients but correctly defined its site in 7 cases only. CT showed a small mass in the distal common bile duct in 1 case, which postoperative histology diagnosed as a malignant carcinoid tumor of the duodenum. The CT findings of carcinoid tumors were a rounded mesenteric mass displacing bowel loops in 4 cases, an infiltrating colonic tumor in 1 case, an apparently intracholedochal mass in 1, a large necrotic mesenteric mass in 1 case. CT showed lymph node involvement in 2 cases, but no liver metastases were found. A carcinoid tumor was diagnosed in 4 patients based on the typical CT finding of a mesenteric mass with radiating soft-tissue density bands resulting in a stellate pattern. No preoperative diagnosis was possible in some other cases because the CT patterns were aspecific and mimicked those of other lesions, namely of tumor of the distal common bile duct, adenocarcinoma of the right colon, submucosal tumor of the distal ileum, large necrotic mesenteric mass. CONCLUSIONS CT is a useful tool in the detection of carcinoid tumors. The correct diagnosis can be made based on the characteristic CT finding of a rounded mesenteric mass. In our experience, however, carcinoid tumors may present with other CT patterns mimicking those of other tumors.