Necrotizing fasciitis and gas gangrene of the lower extremities are two life-threating emergencies and are the most common causes of gas presence in the lower extremity. Rarely the gas presence is secondary to a perforated viscus and especially the colon. Large bowel diverticula are a quiet common disease in western countries and their prevalence increases with age. Also, the possibility of complications is greater in older patients. However, perforated colonic diverticulum seldom presents only with the presence of gas in the lower extremity. We report a case of emphysematous cellulitis of the left thigh caused by a sigmoid diverticulum perforation in a patient with peritoneal carcinomatosis.