Postpneumonectomy syndrome is a rare complication secondary to postsurgical anatomic changes in the pneumonectomy space. Patients present with marked dyspnea on exertion secondary to airflow limitation from proximal airway compression and overdistention of the remaining lung because of mediastinal shift. Postpneumonectomy syndrome is treated by surgical repositioning of the mediastinum. Knowledge of the clinical and radiological features will enable prompt diagnosis and appropriate treatment.