A 34-year-old woman with Marfan's syndrome had severe heart failure due to annulo-aortic ectasia and aortic insufficiency, which was accompanied also by a dissecting aneurysm (DeBakey type IIIb) that was demonstrated by aortography. 4 days before the operation, sudden progression of the aneurysm to a DeBakey type II, and finally DeBakey type I dissecting aneurysm was seen. The first operation was an extended aortic resection with replacement from the aortic valve to the descending thoracic aorta (level of the 7th thoracic vertebra) using selective cerebral perfusion. The second operation was a replacement of the residual dissecting aorta from the level of the 8th thoracic vertebra to the celiac artery with partial extracorporeal circulation. The postoperative course of the patient was uneventful. Dissecting aneurysm with Marfan's syndrome should be operated as extensively as possible if necessary.