Post-traumatic pulmonary pseudocyst is an uncommon cavitary lesion of the lung, which generally develops after blunt chest trauma. We saw a 22-year-old man with chest trauma, hemopneumothorax, and hemoptysis, on the day he fell from an electrical pylon. Intubation in the emergency department was followed by 4 days of mechanical ventilation. Computed tomogram found a post-traumatic pulmonary pseudocyst. On hospital day 6 he developed pneumonia, which we treated with ceftazidime plus gentamycin. He was discharged on hospital day 20, and a month later the pseudocyst had resolved without complications. Diagnosis of post-traumatic pulmonary pseudocyst may require computed tomography, and some complicated cases may require surgery.