The treatment of rectal carcinoma is mainly determined by its local extension, which is difficult to assess before surgery. Our purpose was to determine the reliability of endorectal echography (ERE) in order to provide preoperative assessment of local extension of rectal tumors. Twenty-five patients with rectal adenocarcinoma were included in this study. Seventeen tumors could be felt by rectal examination. ERE was impossible in one case. Echographic data were compared with anatomic findings in 24 patients. ERE provided an accurate assessment of the parietal involvement in 22 cases. The sensitivity and specificity of ERE in determining the spread of the tumor to the rectum alone were 1 and 0.89, respectively, superior to the results provided by clinical examination alone (sensitivity 0.84-specificity 0.76). When the results of the two investigations were identical, all patients were well classified. For lymph node involvement, the sensitivity and specificity of ERE were 0.71 and 0.76 respectively. These results show that ERE is one of the best investigations currently available for assessing parietal involvement of rectal tumors. ERE might be able to determine the appropriate place of radiation therapy, local excision or anal sphincter preservation.