In rectal cancer, the depth of tumor infiltration and metastatic involvement of lymph nodes are important prognostic factors. Endosonography of the rectum, combining the advantages of both endoscopy and sonography, provides information not available from other imaging diagnostic techniques. From January 1989 to December 1997, 85 patients affected by rectal carcinoma were submitted to preoperative evaluation with endorectal ultrasonography. In 75 cases the results obtained with the endosonography were compared to the histology of the resected specimens. Overall accuracy in staging depth of infiltration was 90.7%. Overstaging occurred in 4% of patients, whereas understaging occurred in 5.3%. In staging lymph nodal involvement, overall accuracy was 76%, sensitivity was 69.8%, specificity was 84.4%, positive predictive value was 85.7%, and negative predictive value was 67.5%. Endorectal ultrasound is a safe and accurate diagnostic method for staging both tumor invasion and lymph node metastatic involvement, and for selecting an appropriate surgical strategy in patients affected by rectal cancer.