Pneumomediastinum and subcutaneous emphysema are very rare reported signs of colonic perforation most often associated with diverticulitis, toxic megacolon and colonoscopy. We report a case of a 60-year-old man with subcutaneous emphysema and pneumomediastinum, which developed three days after a car accident without pneumothorax. A computed tomography scan demonstrated perforation of a sigmoid diverticulum in conjunction with air. A laparotomy was performed and revealed a perforated sigmoid diverticulum, fistulized into the retroperitoneal cavity. We suspect that this diverticular perforation was caused by the deterioration of the sigmoid mesocolon secondary to the blunt abdominal trauma. To our knowledge, this is the first report in the literature about pneumomediastinum and subcutaneous emphysema caused by sigmoid diverticular rupture following mesosigmoid trauma.