The capabilities were evaluated of endorectal ultrasound in assessing the local extension of rectal carcinomas. The study population consisted of 50 patients with histologically proven rectal cancer. A CT scan was also performed on 45 patients, and the results were then compared to postoperative histologic findings. Endorectal US allowed the correct staging of 39/45 tumors (86.6%) with 1 false positive (over-staging T1 as T2), and 5 false negatives (under-staging 3 x T3 as T2; 2 x T4 as T3). CT allowed the correct staging of 37/45 tumors (82.2%), with 5 false positives (overstaging T1 as T2) and 3 false negatives (understaging T3 as T2). Our results prove endorectal US to be a reliable method for the local staging of rectal cancers, limited to mucosa, submucosa and muscular layers of the rectal wall (T1 and T2 tumors). CT does not allow proper evaluation of T1 and T2 tumors, but provides with a better assessment of tumors involving perirectal fat and adjacent structures (T3 and T4). Both CT and endorectal US should, therefore, be used as complementary diagnostic techniques for an accurate evaluation of the local extension of lower rectal cancers.