A routine chest radiograph in a 20 year old man revealed a giant air filled cavity of the left hemithorax under tension. At thoracotomy a large left lower lobe intraparenchymal cyst required lobectomy and the pathological findings were consistent with a bronchogenic cyst. Although tension bronchogenic cysts are common in infants, this case demonstrates their unusual presentation in an adult. (Thorax 1993;48:951-952) Large air filled cysts displacing the mediastinum and causing respiratory distress have been reported frequently in infants.1-3 In contrast, giant bronchogenic cysts containing air under pressure have rarely been described in older children and adults.3 6We present an adult with this unusual complication who underwent successful surgical resection.Case report A 20 year old Haitian man who had been living in the USA for one year came to -the tuberculosis clinic for evaluation of a positive tuberculin test. A chest radiograph showed a large cystic lesion occupying most of the left hemithorax, displacing the trachea and the mediastinum to the right (fig 1). He