A mature male beluga whale (Delphinapterus leucas) was presented for examination with signs of subcutaneous emphysema, concurrent with lethargy and anorexia. The emphysema was sudden in onset and rapidly progressive until the animal's death less than 24 hours later. Necropsy findings included extensive emphysema, as well as pneumothorax, pleuritis, pleural rupture and pneumonia. A non-septic chronic type of exudate was found in the thorax, and histopathology revealed that the pneumonic lesions were also consistent with a chronic process. It is proposed that the emphysema was associated with a functionally open pneumothorax, and that pulmonary and pleural rupture were secondary to long standing thoracic adhesions. The purpose of this paper is to describe an unusual clinical and pathological syndrome and to emphasize the diagnostic difficulties associated with cetacean pneumonias.