Postoperative aneurysm of ductus arteriosus is a rare complication but may be lethal without treatment. It is less frequent than spontaneous aneurysm of ductus arteriosus. We report the case of 5 years-old girl who underwent a ligation of patent ductus arteriosus complicated, 6 months later, with a false aneurysm of ductus arteriosus and endocarditis of the ductus and the aortic valve. The diagnosis of the aneurysm was suspected on the anteroposterior chest X-ray which showed a left superior mediastinal opacity and confirmed by echocardiography. Through bilateral thoracotomy, an anevrismorraphy and aortic repair was carried out without problem. The postoperative course was unremarkable.