During a 3-month period an autopsy study was performed on cases of penetration lung trauma to assess the frequency and significance of air embolism. The technique of detecting air in the chambers of the heart and the coronary vessels was, in the early part of the study, to flood the pericardium with water and observe for air while stabbing the heart chambers. Later it was found preferable to manipulate the removed heart in a basin under water. Twelve cases demonstrated injury to the pulmonary parenchyma alone with no other injury, either intra- or extra-thoracic, to account for death. In nine of these cases significant amounts of air were demonstrated in the heart and coronary vessels using our autopsy techniques. Case reports are summarized to emphasize the clinical picture (unexplained hypovolemic shock, cerebral symptoms) and autopsy findings (evidence of air embolism).Successful management requires an awareness of the condition, correction of those factors exacerbating air embolism, and prompt thoracotomy in order to clamp the injured lung pedicle in patients failing to respond to therapy.