A PREVIOUSLY healthy 11-year-old girl had sudden-onset left-sided chest pain in the morning. On physical examination, a normal-appearing girl had tachypnea and shallow respirations. The trachea was shifted to the right, and her breath sounds were decreased in the left thorax. No clubbing of the fingers was present. Findings from frontal chest radiograph revealed a left tension pneumothorax (Figure 1). Her dyspnea was relieved after a left thoracostomy tube was inserted. Computed tomography of the chest disclosed clusters of emphysematous bullae in the left lower lobe (Figure 2). Resection of the bullae was performed using a video-assisted thoracoscope (Figure 3). Her α1-antitrypsin level was 154 mg/dL, which was within reference limits. Results of a pathologic examination of the excised lung showed a prominent emphysematous change with rupture of alveolar septae that resulted in multiple bullous formations (Figure 4). In between the bullae, the lung parenchyma was compressed but structurally normal. The bullae ranged from 0.5 cm to 3.0 cm in diameter without a respiratory epithelium lining.