The optimal preoperative evaluation of periampullary neoplasms remains controversial. The aim of this study was to analyze the accuracy of helical computed tomography (CT) and CT angiography with three-dimensional reconstruction in predicting resectability. Between March 1996 and May 1999, a total of 100 patients with periampullary neoplasms were prospectively staged by helical CT and CT angiography with three-dimensional reconstruction. Vascular involvement was graded from 0 to 4, with grade 0 representing no vascular involvement and grade 4 total encasement of either the superior mesenteric vein or artery. Patients with grade 4 lesions were considered unresectable. Sixty-eight patients underwent surgical exploration with intent to perform a pancreaticoduodenectomy. Forty-four lesions were grade 0, five were grade l, eight were grade 2, and 11 were grade 3. Resectability for grades 0 to 3 was 96%, 100%, 50%, and 9%, respectively, for an overall resectability rate of 76%. Resectability in patients with vascular encroachment (grade 2) is usually determined by the extent of local disease rather than the presence of extrapancreatic disease. Resection is rarely possible in patients with evidence of vascular encasement (grade 3). Additional imaging modalities such as diagnostic laparoscopy are superfluous in patients with no evidence of local vascular involvement on CT angiography (grades 0 and 1) because of the high resectability rate and infrequency of unsuspected distant metastatic deposits.