Hemorrhagic colitis may be seen as a complication of inflammatory bowel disease, as well as infectious colitis related to several pathogens, including enterohemorrhagic E. coli, Shigella, Yersinia and Campylobacter. Also, it is seen in the form of antibiotic-associated hemorrhagic colitis. However, Escherichia coli serotype O157:H7 is now recognized as an important identifiable cause of hemorrhagic colitis. Occasionally, patients with E. coli serotype O157:H7 infection are diagnosed as having thrombotic thrombocytopenic purpura (TTP), a condition similar to hemolytic uremic syndrome (HUS) but with more prominent neurological findings and less renal involvement. We report a case in a 47-year-old woman who developed hemorrhagic colitis complicated by TTP, responded to steroid and antibiotic treatment. (Korean J Gastrointest Endosc 2004; 29:529533)