Deadly Dozen ... Lethal Six ... Hidden Six ... Major thoracic injuries are known as the Deadly Dozen. The Lethal Six (airway obstruction, tension pneumothorax, cardiac tamponade, open pneumothorax, massive hemothorax, and flail chest) are immediate, life-threatening injuries that require evaluation and treatment during primary survey. The Hidden Six (thoracic aortic disruption, tracheobronchial disruption, myocardial contusion, traumatic diaphragmatic tear, esophageal disruption, and pulmonary contusion) are potentially life-threatening injuries that should be detected during secondary survey. Each of these may present as immediately life-threatening or potentially life-threatening events. This article provides an overview of these 12 injuries and appropriate management for each. Case studies are included.