Two cases of fulminant colitis due to Clostridium difficile occurred within ten weeks of each other on the same ward of a hospital in Japan. The patients died 2 and 4 days after the onset of colitis. C. difficile isolates obtained from both patients were toxin A-positive, toxin B-positive and binary toxin-positive. These isolates yielded identical results by both PCR ribotyping and slpA sequence typing. However, the banding patterns and slpA sequences of the isolates differed from those of PCR ribotype 027, as well as those of PCR ribotype 078. The tcdC sequences of the isolate differed from those of C. difficile 027, but a single base-pair deletion at position 117 and an 18 bp deletion, both of which were identical to the sequence of the reference strain of 027, were found. This type may be a new hypervirulent strain, but further studies of the epidemiology and pathogenicity of the strain are needed.