Postpneumonectomy syndrome is a rare entity in children. We report a case secondary to pneumonectomy performed due to an intrathoracic tumor. A 4-year-old boy with a history of right pneumonectomy and progressive respiratory distress, with extrinsic airway obstruction due to displaced mediastinal structures. There were failure to intubate the airway with endoluminal devices and impossibility of withdrawing from mechanical ventilation. As mediastinal repositioning was not possible, an aortic bypass with a prosthetic tube graft was performed, with favorable outcome and hospital discharge.