Pseudomembranous colitis is an inflammatory disease of the colon and rectum characterized by the development of elevated mucosal plaques. It usually is associated with antibiotic therapy and is caused by elaboration of toxin from the anaerobic bacterium, Clostridium difficile. The hallmark of treatment is orally administered vancomycin or metronidazole. The mortality rate is high in patients whose condition is not diagnosed and appropriately treated. Emergency surgery occasionally is needed for complications, including colonic perforation and toxic colitis.