We report a 47-year-old man with acute leukemia who survived a severe case of necrotizing fasciitis caused by Clostridium perfringens involving his right upper extremity. On day 5 after stem cell transplantation, progressive local tissue necrosis led to septicemia and disseminated intravascular coagulation. Early diagnosis and prompt initiation of appropriate therapy, including surgical debridement and broad-spectrum antibiotics, were crucial. A recombinant thrombomodulin might have not only resolved the coagulation problem but also prevented multiple organ failure associated with the systemic inflammatory response.