Chest trauma is one of the most serious and difficult injuries, with various complications that can lead to ventilation - perfusion (V/Q) mismatch and systemic hypoxia. We are presenting a case of 53 – year - old male with no comorbidities or chronic therapy, who was admitted to the Intensive Care Unit due to severe respiratory failure after chest trauma. He developed right - sided pneumothorax and then thoracic drain was placed. On admission, the patient was hemodynamically unstable and tachypneic. The patient was intubated and mechanically ventilated, febrile (38.9°C) and unconscious. A lung CT showed massive non-ventilated areas predominantly in the right lung. He was ventilated with PEEP of 10 cmH2O with a FiO2 of 0.6 – 0.8. Empirical broad-spectrum antimicrobial therapy was immediately initiated. Both high FiO2 and moderate PEEP were maintained and adjusted according to the current blood gas values and oxygen saturation. After Stenotrophomonas maltophilia was identified and treated with sulfamethoxazole/trimethoprim his general condition gradually improved, and he was weaned from mechanical ventilation. In conclusion, both ventilatory and antibiotic therapy were needed to improve oxygenation and outcome of the patient with pneumonia due to the resistant S. maltophilia with V/Q mismatch.