Tension pneumothorax is a life threatening condition which requires prompt diagnosis and treatment. We report a case of delayed tension pneumothorax caused by blunt chest trauma, which was diagnosed intraoperatively and successfully treated by chest tube insertion. In this case, the tension pneumothorax was thought to be due to blunt chest trauma and precipitated by positive pressure ventilation during anesthesia. The diagnosis and treatment of intraopetative pneumothorax is discussed together with a review of the literature.