Digital examination and computed tomography are the current modalities employed to assess the depth of invasion of rectal cancer. Each technique has limitations in that high rectal tumors cannot be examined digitally and CT is unable to detect small tumors. However, preoperative diagnostic capability can be improved with the use of intrarectal ultrasound. We have examined 25 patients with rectal cancer preoperatively with digital examination and intrarectal ultrasound. In order to determine the accuracy of the ultrasonic method, we compared the results to the histopathologic findings of the excised specimen. Digital examination was essentially impossible in eight of the 25 rectal tumors because the tumors were either unreachable or could not be palpated in their full longitudinal extent. Of the remaining 17, digital examination corresponded with pathologic findings in 15, while tumor spread was overestimated in two patients. Sonography corresponded with pathologic findings in 23 of the 25 tumors. Two had been overstaged. Analogous to the TNM classification for postoperative pathologic tumor staging, we propose a preoperative tumor staging based on ultrasonic determination of the infiltrative depth of tumor, which we call u TNM.