PURPOSE: In patients with colorectal carcinoma, helical CT using air as a contrast agent provides axial images and a three-dimensional CT colonogram similar to that provided by barium enema. The purpose of this study was to assess the usefulness of air insufflation helical CT in colorectal cancer patients. MATERIALS AND METHODS: Thirty-three patients with colorectal carcinoma confirmed by surgery underwent air insufflation helical CT scanning after the infusion of air through the anus. In eleven who underwent barium studies, CT colonograms were also obtained. Two radiologists, who reached a consensus, analysed the detection rate, location and staging of the tumors; staging was based on the modified Dukes (Astler-Coller) classification. RESULTS: Using axial helical CT, the detection rate was 97%; staging was correct in 23 of the 33 patients, with an overall accuracy of 70%. Pathologic correlation was correct in 30 of the 33 cases (three were overestimated), and sensitivity, specificity and accuracy were 100%, 50%, and 91%, respectively. With regard to the involvement of lymph nodes, pathologic correlation was correct in 25 of the 33 patients; four were overestimated and four were underestimated. Sensitivity, specificity and accuracy were 69%, 80%, and 76%, respectively. The detection rate of CT colonography was 100%, but because in one case there was a discrepancy between CT colonography and barium enema as to the shape of the carcinoma, the agreement rate was 91%. CONCLUSION: Air insufflation helical CT, which provides a higher detection rate and more precise staging of colorectal carcinoma than the use of positive contrast materials and three dimensional depiction of tumor location, is helpful for the evaluation of colorectal carcinoma.