Cap polyposis is a rare disorder characterized by bloody, mucoid diarrhea with rectosigmoid polyps covered by a cap of fibrinopurulent exudate. The etiology and pathogenesis of cap polyposis is unknown, and no specific treatment has been established. Drug therapies are usually unsuccessful. Patients with a solitary cap polyp respond well to endoscopic polypectomy, while patients with multiple polyps and concurrent anorectal pathology require surgical resection. However, rapid recurrence has been described after a limited surgical resection, and this necessitates panproctocolectomy. We report a case of a 58-year-old female diagnosed as cap polyposis on rectum with similar clinical and endoscopic features of pseudomenbranous colitis successfully treated with infliximab (murine chimeric monoclonal antibody to TNF-α). (Korean J Gastrointest Endosc 2005;31:180184)