From March 1998 to May 2002, we experienced 46 patients with type A acute dissection (AAD). Fifteen patients managed initially with conservative treatment because of intramular hematoma (IH, n = 10), broad cerebral infarction (n = 3), others (n = 2). One who diagnosed IH at admission progressed to AAD and underwent surgery. However his diagnosis of IH at admission was proved to be misdiagnosis retrospectively. In 8 of the remaining 9 patients, hematoma disappeared during the follow-up of 6 months to 1 year. In patients with broad cerebral infarction, 2 died early after admission and 1 discharged with hemiplegia. Thirty-two patients underwent surgery and 1 with preoperative broad cerebral infarction died 36 days after surgery. In the remaining 31 patients, 30 patients discharged ambulatory.