Aneurysm of the diverticulum of the ductus arteriosus is a rarely reported entry in adult. To our knowledge, only two previous patients underwent successful aneurysmectomy in Japan. Three new cases of aneurysm of the ductus arteriosus diverticulum in the adult, all diagnosed preoperatively and successfully repaired, are presented. All three patients are alive 17 to 44 months postoperatively. Our experience with these patients suggests several important features of these aneurysms: (1) CT scanning with contrast enhancement will almost invariably confirm the diagnosis of these aneurysms. (2) Exposure through a median sternotomy is generally good and carries less operative morbidity from rupture than a posterolateral thoracotomy. (3) Because of their critical location and the high incidence of rupture in reported cases, aneurysms producing symptoms, or those showing progressive enlargement should be surgically resected. (4) When a succular aneurysm of the aortic arch is demonstrated expanding toward the aortopulmonary window with adhesion to the pulmonary artery, the possibility of its origin from the ductus arteriosus must be investigated.