Backgrounds: Intramural hematoma of the aorta (IMH) evolves very dynamically in the short term reabsorption, classical dissection, or aortic rupture. The aim of this study was to evaluate the clinical outcomes and morphological evolution according to Stanford classification. Material and Methods: We analyzed 118 consecutive medically treated patients with acute IMH from four large centers in Daegu. The patients were grouped according to Stanford classification. Type A IMH were 44 (37.3%) and type B IMH were 74(62.7%). A follow-up contrast enhanced computed tomography (CT) was performed in 89 (75.4%) patients within 30 days. Clinical outcomes such as death, surgical conversion and morphological evolution by CT were analyzed. Results: In-hospital mortality rate were not different between type A and type B IMH (3/44, 6.8% vs. 2/74, 2.7%, p=0.36). The follow-up CT study showed that intramural hematoma was resorbed in 20 patients with type A IMH and in 36 patients with type B (20/35, 57.1% vs. 36/54, 66.7%, p=0.194). Progression to aortic dissection was common with type A comparing type B IMH (6/44, 13.6% vs. 2/74, 2.7%, p=0.051). Surgical conversion was more needed because of aortic dissection or progressive aortic dilatation in type A IMH (6/44, 13.6% vs. 1/74, 1.4%, p=0.011). Mean follow-up duration was 877짹906 days. The 2-year survival rate was 81.8% in the type A IMH and 87.8% in the type B IMH (p=0.421). Conclusion: Initial medical treatment and timely surgical intervention showed similar clinical outcomes in both types of acute IMH. But, large randomized trial is needed to clarify the optimal treatment modalities of acute IMH. Key Words : Intramural hematoma, clinical outcomes, morphological evolution