Clostridium difficile is the most common cause of nosocomial diarrhea. It is a Gram positive bacillus when viewed microscopically after Gram’s stain. Clostridium difficile associated diarrhea (CDAD) almost always occurs after antibiotic use. Most antibiotics inadvertently denude the gastrointestinal tract of resident colonizing bacteria. If a patient with altered gastrointestinal tract flora is exposed to Clostridium difficile, an infection of the colon by this toxin producing bacteria may result. Typically this leads to diarrhea although in some cases a serious life-threatening infection called toxic megacolon results. Treatment is typically with orally administered metronidazole or vancomycin. In some patients with toxic megacolon surgical removal of the colon (colectomy) is required.