A young male patient with traumatic lung cyst, a rare lesion of blunt chest trauma, is presented. Compression of an elastic thorax with narrowing or closure of the airway produces a bursting or shearing force that creates an intrapulmonary cavity. The cyst may be filled with blood and is often associated with pulmonary contusion. The diagnosis is one of exclusion, based on an awareness that lung cyst can develop after trauma. Chest computerized tomography, as in the case described, may be useful to further delineate the lesion. Patients with traumatic lung cyst should be watched for respiratory distress, but the clinical course is usually uncomplicated, and the lesion completely resolves in 2 to 4 months. There are two indications for surgical treatment: infection in the cavity that is unresponsive to a trial of appropriate antibiotic therapy, and a cavity that does not progressively become smaller. In the patient presented, lobectomy was done 9 days postinjury and the cyst removed, and his subsequent recovery was without problems.