This report analyzes the detection rate and role of CT in the preoperative evaluation of 90 consecutive, proved cases of colon carcinoma. In this study, the overall detection rate was 84%; however, the rate varied from 68% in unprepared colons to 95% in clean colons that were adequately distended with air. Sensitivity of detection depends mainly on the size of the lesion and the quality of the examination. CT was less sensitive than barium enema in detection, but it had a similar specificity in differentiating neoplastic lesions from inflammatory lesions. On the basis of our criteria of staging, CT evaluation resulted in a sensitivity of 55% for local invasion, 73% for regional nodes, and 79% for liver metastases. Compared with Dukes classification, CT correctly staged 64% of all patients but showed significant variations in staging different groups with lower results in the Dukes A, B, and C patients. CT, however, showed a sensitivity of 81% and a positive predictive value of 100% in detecting Dukes D lesions. In general, although negative CT findings do not help in staging a colonic tumor, positive findings are highly indicative of neoplastic spread. We believe that this feature justifies the use of CT in the preoperative evaluation of colonic tumors.