['Clostridium difficile-associated diarrhea (CDAD) is a well-known iatrogenic infection with typical endoscopic features including pseudomembranes and intervening normal mucosa. Clinically, diarrhea frequently occurs, but occurrence of hematochezia is rare. The objective of this study was to investigate the background and endoscopic features of CDAD patients with hematochezia.', 'The endoscopic and clinical findings in 12 patients who showed evidence of C. difficile toxin A and who underwent colonoscopy between April 2002 and July 2007 were investigated retrospectively.', 'Eight patients were diagnosed as having CDAD and 4 patients had a diagnosis of ulcerative colitis. Six of the patients with CDAD presented with hematochezia, and 4 of them were diagnosed with hematological malignancies and received anticancer chemotherapy. Colonic ulcer was demonstrated in all CDAD patients with hematochezia, and bleeding from the ulcer was endoscopically confirmed in all of them.'] Is clostridium difficile-associated diarrhea with hematochezia associated with ulcer formation?