Twenty seven patients with known rectal cancer were evaluated with CT and CT findings were correlated with surgical and pathologic results on the aspect of perirectal fat infiltration and lympy node involvement. The accuracy in assessment of perirectal fat infiltration was 77.8% (21 of 27); sensitivity, 73.3% (11 of 13); specificity, 83.3% (10 of 12). In the detection of lymph node involvement, lymph nodes were divided into five groups according to the arterial teritories. Overall accuracy in the evaluation of lymph node involvement was 86.7%. Accuracy of peritumoral lymph node involvement was 51.9% (14 of 27); sensitivity, 42.9% (9 of 21); sensitivity, 85.7% (6 of 7); specificity, 90.0% (18 of 20). Of the common and external iliac lymph node, accuracy was 100% (27 of 27); sensitivity, 100% (2 of 2); specificity, 100% (25 of 25); sensitivity, 50% (2 of 4); specificity, 100% (23 of 23). In regard to the inferior mesenteric lymph node, no lymphadenophthy was found on CT and path logic results. In conclusion, CT has limited value in evaluating rectal cancer but with the satisfactory outcome in assessment of perirectal fat infiltrastion and lympy node, involvement except peritumoral node preoperative CT is useful in the evaluation of rectal cancer.