We report a patient who, 3 months after being diagnosed with ulcerative colitis, was admitted to hospital because of malaise and right lower abdominal pain. An open appendectomy was performed. Histological study showed ulcerative colitis affecting the appendix. After surgery, the patient presented a refractory outbreak of ulcerative colitis requiring treatment with steroids and cyclosporin A. Despite this treatment, the patient continued to pass abundant fresh blood associated with severe anemia. Colonoscopy showed only granular and congestive cecal mucosa. Biopsies showed intracytoplasmic inclusion bodies with immunohistochemical stains positive for cytomegalovirus (CMV) infection. Rectorrhagia and anemia quickly disappeared after beginning treatment with ganciclovir. Appendicular ulcerative colitis is not uncommonly associated with distal colitis. In addition, diffuse CMV infection complicating ulcerative colitis treatment is not unusual. By contrast, isolated, segmentary infection by CMV in the proximal colon is extremely rare. Until now, only three patients with localized CMV infection have been described, and all three cases occurred in the context of ileoanal anastomosis.