Secondary infection of post-traumatic cavitary lung lesions is unusual. This report describes the clinical course of four patients who sustained severe blunt chest trauma and developed pulmonary pseudocysts that became foci for systemic sepsis. All four patients were adolescents or young adults. Hemophilus species and aerobic Gram-negative rods were the predominant pathogens recovered. Computed tomography of the chest was instrumental in establishing the diagnosis in each case. Despite appropriate antibiotic therapy, all four patients remained septic for weeks. One of the patients died as a result of this infectious process. One patient underwent successful operative debridement and drainage of the involved lung and pleural space. Because infected traumatic pseudocysts may not respond like typical lung abscesses to appropriate antibiotic management, early exploratory thoracotomy should be considered in those patients with prolonged fever and pulmonary deterioration.