A group of 86 patients with anorectal Crohn's disease were followed up from ten to 40 years to determine the course of the disease and the number of patients who later required proctectomy. The overall cumulative probability of avoiding proctectomy was 91.6 percent at ten years and 82.5 percent at 20 years. Resection of all proximal Crohn's disease did not ameliorate the anorectal disease, except in patients who had all proximal disease removed and had no recurrence.