A routine chest radiograph in a 20 year old man revealed a giant air f
illed cavity of the left hemithorax under tension. At thoracotomy a la
rge left lower lobe intraparenchymal cyst required lobectomy and the p
athological findings were consistent with a bronchogenic cyst. Althoug
h tension bronchogenic cysts are common in infants, this case demonstr
ates their unusual presentation in an adult.