Conclusions: lung contusion was common in severe polytrauma, blood sputum that suggested lung contusion occurred in 45% of patients, chest X ray on admission could omit lung contusion at 34.2% of patients, but 24 hours after trauma, lung contusion could be seen on chest X ray at 100% of patients, mean of time from trauma to severe respiratory failure due to ALI / ARDS that needed mechanical ventilation was 18 hours.