We encountered 5 cases of delayed massive hemothorax due to diaphragmatic injury. Delayed hemothorax presented 2∼11 days after injury, with lower rib fractures seen all cases. We performed emergent video-assisted thoracic surgery with mini-thoracotomy for all patients. Lacerations could be clearly visualized in the diaphragm after evacuation of blood clots, which were then sutured. In four cases, the sharp edges of the broken ribs were thought to have caused the diaphragmatic lacerations. The mean blood loss volume was 2,905 ml, and all patients required blood transfusions. However, homeostasis was achieved after surgery, and all patients had an uneventful postoperative course. Although, delayed hemothorax is relatively uncommon, it needs to be considered a lethal condition.