Computed tomography (CT) of the colon is useful in assessment of patients with colonic disease because the entire bowel wall, extraluminal tissues, and adjacent solid organs can be directly visualized. Patients with advanced stage colorectal carcinoma can be reliably identified with CT. This information can assist in surgical planning for intraoperative irradiation and placement of a hepatic artery infusion catheter. CT is an important imaging modality in the postoperative evaluation for recurrent rectal cancer after abdominoperineal resection. CT-guided biopsy often can provide histologic proof of suspected tumor recurrence or metastasis. Patients with diverticulitis or appendicitis can be identified by CT. The extent of disease and the nature of the inflammatory process--factors potentially affecting patient management--can be directly visualized. Percutaneous aspiration and drainage of abscess collections can be curative in appropriately selected patients.