Enteritis necroticans 'pigbel' is caused by Clostridium perfringens type C but has rarely been reported in developed countries. A 50-year-old Japanese man with untreated diabetes mellitus (DM) presented with diarrhea and abdominal pain. Intraoperative endoscopic and macroscopic examination disclosed segmental annular mucosal lesions characteristic of clostridial enteritis. Clostridial infection type C was verified on pathological, and immunohistochemical analysis. Although rare, the disease is likely to be underdiagnosed. Hence, the pathology and immunohistochemistry of segmental enteritis with annular mucosal lesions should be examined to establish a diagnosis of enteritis necroticans even in mildly affected patients, and especially those with DM.