Pulmonary contusion is the usual manifestation of lung parenchymal injury following blunt chest trauma. With rapid deceleration, however, parenchymal lacerations can result in cavities best termed post-traumatic pulmonary pseudocyst (PPP). This report discusses eight adult PPP cases encountered at the Denver General Hospital over the past 30 months. Five were males and the mean age was 29 years (range, 18 to 54). Injury mechanism was motor vehicle accident in four, industrial machinery in two, autopedestrian accident in one, and large-animal rodeo rollover in another. Review of daily portable anteroposterior chest roentgenograms revealed parenchymal infiltrates consistent with pulmonary contusion that typically cavitated within the first week. Computed tomography of the chest was pursued in complicated patients and clearly influenced therapy. Three (38%) pseudocysts developed into lung abscesses; two required resection and the other responded to percutaneous drainage. Although previously described as a benign pediatric entity, in our adult experience, PPP may result in a recalcitrant lung abscess requiring aggressive intervention.