From 1995 till 1998, 21 cases of Stanford type A dissecting aortic aneurysm with a closed false lumen of the ascending aorta were treated in our institute. The patients were medically treated if the diameter of their ascending aorta stayed less than 50mm without recurrent dissection. Patients were categorized into three groups: Groups I, II and IIIR (retrograde dissection), according to the location of the entry analyzed by means of CT, angiography and operative findings. Seven cases of intramural hematoma (IMH) were included in this study. One case in Group II died of rupture and one case in Group IIIR died of multiple embolism caused by atrial fibrillation in the acute phase. One case in Group II died of stroke and one case in Group I died after surgery in the chronic phase. Four cases in Group I and II underwent surgery in the acute phase and five cases in Group I and II underwent surgery in the chronic phase, but only one case of Group IIIR required surgery. Six cases of IMH required surgery. The rates of freedom from operation at four years was 25%, 21% and 83% respectively (p=0.07). Essentially, Stanford type A dissection should be treated surgically even though the false lumen is thrombosed. However, in the case of retrograde dissection accompanied by an entry in the descending aorta, medical treatment may be a strategy option.