A prospective study was designed to evaluate multiple rectal biopsy examinations for dysplasia in 34 patients who had ileorectal anastomosis performed, following colectomy for inflammatory bowel disease. Although all but eight patients had persistent inflammatory activity on histologic examination, only one patient who demonstrated villous transformation of the mucosa clinically, showed carcinoma in situ in the excised rectal specimen. A protocol for surveillance of preserved rectums in inflammatory bowel disease is offered.