Background: Data regarding the outcome of type A aortic intramural hematoma (AIH) are based on relatively small number of the subjects and controversial opinions for treatment option are available. Methods and results: We evaluated 357 patients with type A acute aortic syndrome (AAS) managed in our center between April 1993 and March 2008 to delineate clinical features, management, and outcomes of acute AIH by comparing these patients with those with classic aortic dissection (AD). One hundred one (28.3%) patients had AIH with higher mean age (65짹10 versus 56짹14 years, p<.001) and higher prevalence of hypertension (67.3% versus 52.3%, p<.001) compared with 256 patients with AD. Eighty five (84.2%) patients with AIH received initial medical treatment and among them 25 patients (29.4%) underwent timed surgery during admission due to various reasons including development of AD (n=10) and increase of hematoma thickness (n=7). Overall in-hospital mortality was lower in AIH (7.9% versus 17.2%, p=0.025) and markedly lower mortality was observed in patients without emergent surgery (7.1% versus 63.3%, p<.001). The 30-month cumulative survival rates according to the treatment options were not different in AIH group, whereas significant difference was observed in AD group. Conclusions: AIH comprised significant proportion of type A AAS and showed different clinical features and more favorable response to medical treatment compared to classic AD. Contrary to AD, survival benefit of emergent surgery could not be confirmed in AIH.