Abstract Background: Accurate preoperative staging of rectal lesions can help select patients for treatment options. This prospective study examines the effects of endorectal ultrasonography (ERUS) in the management of resectable adenomas and adenocarcinomas. Methods: Between November 1995 and August 1998, 34 patients had resection of their rectal lesions (28 adenocarcinomas, 6 adenomas). Preoperative clinical stage and surgical and adjuvant therapy plans were specified before ERUS staging; then comparisons were made to postoperative pathologic stage and actual treatment. Results: ERUS helped select 7 of 11 patients (64%) for preoperative chemoradiation therapy. Treatments of adenocarcinomas were altered by ERUS to local excision (LOC) in 4 of 9 patients (45%) planned for low anterior resection (LAR), and 2 of 10 patients (20%) planned for abdominoperineal resection (APR). ERUS helped spare 2 patients with adenoma from APR. Conclusion: ERUS is a useful modality in the surgical management of patients with rectal adenomas and carcinomas.