"본 논문은 대한영상의학회지 2005년 제52권 제1호에 실렸던 논문으로 대한영상의학회의 승인을 득하고 본 협회지에 게재함. Purpose: We wished to compare CT colonography with conventional colonoscopy for the detection of colorectal poiypoid lesions, and we wanted to evaluate the role of IV contrast-enhanced CT colonography for the differentiation between benign polypoid lesions and malignant polypoid lesions. Materials and Methods: Thirty-four consecutive patients underwent CT colonography prior to conventional colonoscopy, Precontrast prone-position CT images and post contrast supine position CT images were obtained and the virtual colonoscopic images were reconstructed, Axial, sagittal and presence, size and morphologic features of colorectal polypoid lesions, and thor these findings were compared with the colonoscopic findings. The degree of enhancement of colorecralpolypoid lesions was measured by subtracting the attenuation valves obtained with precontrastand postcontrast CT images for the differentiation of benignity and malignancy of the colorectal polypoid lesions. Results. Among 75 colorectal polypoid lesions identified on conventional colonoscopy, 49neoplasms were found on CT coloaographv, and the overall detection rate was 65,3%.Detection rate of lesions smaller than l0mm was 52.1%(24/46), and the detection rate for lesions equal to or larger than 10mm was 86.2%(25/29), Morphologic features of the sessile type lesions on CT colonography were well correlated with those noted on colonoscopy, but the stalks were not identified in 6 of 13 polyps on CT colonography. There was no statistical correlation between benignity and malignancy and the degree of contrast enhancement on CT colonography, Conclusion CT colonography is a useful modality for the detection of colorectal polypoid lesionsequal to or polyps. However, CT colonography cannot differentiate benignity from malignancy.