Purpose : To evaluate the usefulness of the arterial dominant phase images of spiral CT in the detection andlocalization of pancreatic islet cell tumor. Materials and Methods : Six patients with pathologically proven isletcell tumors of the pancreas were studied with two-phase spiral CT. Images of the arterial dominant phase anddelayed phase were obtained at 30 and 180 seconds after the initiation of injection of 100 ml of contrast materialat a rate of 3ml/sec. The parameters of scanning were 3-mm thickness, table speed of 4mm/sec, and reconstructionat 2-mm intervals. Images were prospectively analyzed and the operative findings were used as the referencestandard for tumor detection and localization. Results : On arterial dominant phase images, lesions weredefinitely depicted in five patients(83%) and were suspicious in one (17%). In the delayed phase, only twotumors(33%) were demonstrated. Conclusion : The arterial dominant phase of spiral CT is useful in the preoperativedetection and localization of islet cell tumor of the pancreas.