Sixty-three patients with chronic ulcerative colitis and 80 patients with Crohn's disease underwent abdominal colectomy and primary ileorectal or ileosigmoid anastoimosis and were followed up for between five and 17 years. No patient developed carcinoma of the rectal stump. The interval proctectomy rate was similar in both groups (24 and 29%, respectively), the rate being influenced by age in the group with chronic ulcerative colitis. The young patients with ulcerative colitis required proctectomy more often than did the patients with onset later in life. The proctectomy rate was not influenced by the level of the anastomosis. In patients with normal or moderately diseased rectal mucosa, the preoperative condition of the rectum did not influence the proctectomy rate. Functional results were satisfactory in 55% of the patients with chronic ulcerative colitis who survived and in 35% of the patients with Crohn's disease who survived. Because of the non-curative nature of surgery for Crohn's disease, a conservative posture should be maintained, with preservation of normal or moderately diseased rectal segments. If sigmoidoscopie examination and biopsy are done periodically, abdominal colectomy and ileorectal or ileosigmoid anastomosis appears to be a viable option to proctocolectomy in selected patients with chronic ulcerative colitis.