Hemorrhagic colitis due to Escherichia coli O157:H7 is a distinct clinical entity characterized by abdominal pain, watery diarrhea progressing to bloody diarrhea, and little or no fever. It has been reported to have a mortality as high as 31%. This form of colitis is not described in the radiologic literature. This paper describes the radiographic findings, and stresses the need for radiologists to be familiar with the disease in order to assist in early diagnosis. Key clinical and epidemiological features are reviewed.