Admission chest x-ray of an 81 year-old man admitted to the hospital for atrial fibrillation with rapid ventricular response is shown in Figure 1. The chest x-ray shows a unilateral hyperlucent lung, with paucity of peripheral vessels and decreased lung volume. Differential diagnosis for unilateral hyperlucent lung includes Swyer-James-McLeod syndrome (SJMS), centrilobular emphysema, allergic bronchopulmonary aspergillosis, congenital lobar over inflation, bronchial atresia and congenital interruption of pulmonary artery.1 High resolution CT imaging confirmed the diagnosis of SJMS in this patient.