PURPOSE: To assess the diagnostic value of the use of multi-detector row computed tomography (MDCT) in evaluating mesorectal fascial (MRF) involvement in patients with T3 stage rectal cancer. MATERIALS AND METHODS: From September 2005 to June 2006, we enrolled 21 patients with T3 stage rectal cancer. In addition, 21 healthy patients were enrolled in a control group. Two radiologists measured the mean MRF thickness independently. We considered positive MRF involvement when the MRF thickness exceeded 4 mm, and then we measured the MRF thickness of patients with T3 rectal cancer. We analyzed interobserver agreement for the measured MRF thickness of the control group and assessed the diagnostic value of 4 mm, 5 mm and 6 mm as references in predicting MRF involvement. RESULTS: The mean MRF thickness of the control group was 3.24+/-0.50 mm (radiologist 1) and 3.04+/-0.51 mm (radiologist 2). Using 4 mm, 5 mm and 6 mm as a reference thickness in predicting MRF involvement, sensitivity was 100%, 100% and 28.57%, specificity was 71.43%, 85.71% and 92.86%, the false negative rate (FNR) was 0%, 0% and 71.43%, the false positive rate (FPR) was 28.57%, 14.29% and 7.14%, the negative predictive value (NPV) was 100%, 100% and 72.2%, the positive predictive value (PPV) was 63.64%, 77.78% and 66.7%, and the accuracy was 80.95%, 90.48% and 71.43%. CONCLUSION: Preoperative assessment of the MRF thickness on MDCT is beneficial in predicting MRF involvement in patients with advanced rectal cancer and a value of 5 mm as a reference MRF thickness was established.