Nontraumatic subcutaneous emphysema is a rare complication of colorectal cancer. To the authors' knowledge, only eight cases have been reported to date. The initiating event was free colonic perforation in seven of the patients and contained colosubcutaneous fistula in the eighth. In nontraumatic subcutaneous emphysema typical fecal flora is cultured, whereas in nontraumatic gas gangrene, a different clinical entity that has a fulminant course, the bacteria are generally clostridial. The authors report a case of nontraumatic subcutaneous emphysema associated with rectal carcinoma and describe the associated computed tomography findings.