Two cases are described in which chest radiographic findings were typical of those reported as "pneumatocele in the pulmonary ligament" in adults. Analysis based on lateral chest radiography and computed tomography showed a loculated hydropneumothorax behind the pulmonary ligament. Review of the literature failed to show any cases with a lateral radiograph inconsistent with this interpretation. Middle mediastinal air in the newborn, which appears quite different on the lateral chest radiograph, may extend into the pulmonary ligament, though this is unproved. There is probably no such entity as "pneumatocele in the pulmonary ligament" in the adult.