A 29-year-old female with ulcerative colitis was found to have advanced sigmoid colon cancer on colonoscopy. Computed tomography (CT) was performed after colonoscopy for the evaluation of metastasis. CT colonography (CTC) could be understood adding carbon dioxide because of soon after colonoscopic examination. Images of CTC were evaluated by two- and three-dimensional images including virtual endoscopic, virtual colon dissection and air images, and then compared with conventional endoscopic images. Virtual endoscopic images of flat elevated cancer with shallow ulcer were similar to those findings by conventional endoscopy. This lesion could be depicted by computer-aided detection.