This study reports a 4 year experience using CT for preoperative staging and for evaluation of patients with rectal and sigmoid carcinoma after surgery. All patients were evaluated on a GE 8800 scanner using 1 cm contiguous slices. Only 15 of the 25 preoperative patients were staged correctly. The other 10 patients were understaged by CT. The accuracy of detecting local invasion was 70%, but only seven (35%) of 20 patients had accurate assessment of lymph nodes. The overall accuracy of CT staging in the 46 postoperative patients was 87%, with a sensitivity of 91% and a specificity of 72%. Most recurrences were found in the pelvis; 16 patients had liver metastases, and metastatic disease obstructing the ureters was detected in eight patients. On the basis of these results, it was concluded that CT should not be used routinely to preoperatively stage patients with rectosigmoid carcinoma. However, all patients who have undergone resection for rectal or sigmoid carcinoma should have aggressive CT evaluation including a baseline study at 2-4 months and then follow-up studies at every 6 months for at least 2 years. All new or enlarging masses should have CT-guided biopsies. This approach may prolong survival by detecting early asymptomatic recurrences.