We retrospectively compared the CT findings in patients with and without surgically proved small-bowel obstruction to evaluate the role of CT in diagnosing the presence and cause of obstruction. In the patients with obstruction, we compared the CT findings with findings on plain abdominal radiographs and contrast studies of the small intestine. CT criteria used for the diagnosis of obstruction were dilated small-bowel loops proximal to the suspected site of obstruction and collapsed or normal-appearing loops of small bowel distal to the obstruction. Receiver-operating-characteristic analysis suggested the optimum balance of sensitivity and specificity was achieved when 2.5 cm was used to indicate dilatation of the small bowel. On the basis of these criteria, the presence of obstruction was correctly diagnosed in 27 (90%) of 30 patients with proved obstruction, and obstruction was not diagnosed in the patients without obstruction. The cause of the obstruction was evident on CT in 14 of the 30 obstructed patients: abscess (five), neoplastic lesion (three), peritoneal carcinomatosis (three), and other (three). Adhesions were responsible for the obstruction in 13 of 15 patients in whom the cause was not shown on CT. In six patients in whom findings on plain abdominal radiographs were normal, the CT scan was positive for obstruction. However, in the three patients whose CT scans were falsely negative for obstruction, findings suggesting obstruction were seen on plain films. Of 15 patients who had both CT and contrast studies of the small intestine, CT offered more information concerning the cause of obstruction in six (40%), primarily by demonstrating significant extraluminal abnormalities. CT and gastrointestinal contrast studies gave concordant results in eight patients with obstruction. In only one patient did the gastrointestinal contrast study give more diagnostic information. We conclude that CT scanning demonstrates accurately the presence of high-grade small-bowel obstruction and may be the technique of choice when extraluminal abnormalities are suspected or when prompt, efficient, and comprehensive evaluation is required.