We present here the case of a 75-year-old woman who complained of acute abdominal pain after a diagnostic colonoscopy. Abdominal x-rays demonstrated pneumoperitoneum, whereas chest x-rays showed pneumomediastinum and left pneumothorax. A chest drain was placed and subsequently an exploratory laparoscopy was performed, during which air was found in the subserosa of the sigmoid colon and in the mesosigmoid secondary to perforation of a sigmoid diverticulum. The perforation was repaired and a protective loop colostomy was fashioned. The patient was discharged 8 days postoperatively in a good general condition. Although numerous cases of pneumoretroperitoneum and pneumomediastinum secondary to iatrogenic perforation of the colon have been described, reports of pneumothorax are much rarer. We, therefore, discuss the anatomic bases and the possible physiopathologic mechanisms responsible for this clinical complication.