Summary and ConclusionsRegional colitis may involve any segment of the colon with or without concomitant involvement of the small bowel. It is an entity, separate and distinct from ulcerative colitis. Usually the correct diagnosis can be established by clinical, radiologic and histologic examination.Careful rectal biopsy, or microscopic examination of tissue removed from anal and perianal lesions, may reveal granulomas or sarcoid reactions typical of the disease.Because most patients with regional colitis limited to thecolon onlydo very well after surgery, prompt resection and anastomosis is advocated.In regional colitis, the rectum should be preserved if possible, even if a temporary ileostomy is required in order to treat severe perianal lesions. There is little danger that the rectum will become involved by carcinoma or that systemic complications such as arthritis, uveitis, pyoderma and hepatitis will occur.