Pretherapeutic staging before radiotherapy and peri- and posttherapeutic endosonographic screening was carried out on 33 patients with anorectal carcinoma. The results showed the transrectal endosonography to be essential for staging and for the differential diagnosis of tumor recurrence/post irradiation changes during follow up. The sonomorphological criteria of tumor recurrences and post irradiation bowel wall changes are discussed.