Purpose : To analysis the radiologic characteristics of a pancreatic islet cell tumor, and to assess the usefulness of spiral CT scanning in the detection of a small tumor. Materials and Methods : We retrospectively reviewed the clinical, pathologic, and imaging features of 12 cases of pathologically-proven islet cell tumors of the pancreas occurring between 1989 and 1995. Imaging study included conventional CT (n=9) , spiral CT (n=3), ultrasonography (n=5), MRI (n=4), and angiography (n=6). Results : Among 12 patients, eight (67%) were diagnosed as suffering from functioning islet cell tumor, and four (33%) as nonfunctining tumors cases. Of the former, four were insulinoma and one was glucagonoma. Their average diameter was 2.4cm, whereas that of nonfunctioning tumors was 5cm. The average diameter of islet cell tumors was 1.3cm. Using conventional CT (4), spiral CT (3), ultrasonography (3), MRI (1), and angiography (3) preoperative localization was possible. Dynamic spiral CT scans with 5mm slice thickeness were performed in the three cases of smaller tumor (2cm) showed 100% sensitivity. Conclusion : Since nonfunctioning islet cell tumors tend to be large, it is usually possible to detect a tumor by using only ultrasonography or conventional CT scan. In the case of functioning islet tell tumors, however, localization of the lesion requires more complicated imaging studies. Our results show that thin slice spiral CT was valuable in the defection of small functioning tumors and can be the modality of choice for preoperative localization of a pancreatic islet cell tumor.