Purpose: The intramural hematoma is known as a precursor of aortic dissection but shows better prognosis compared with aortic dissection itself. In our institute, all patients with aortic disease were studied by CT angiography during past 11 years. This study was designed to reveal the correlation of CT finding and the clinical outcomes of IMH and the natural course of IMH in follow up CT angiography. Materials and Methods: For 11 years, there were total 87 patients with acute intramural hematoma out of 383 patients with aortic dissection, diagnosed by CT angiography. We analyzed the CT angiographic findings in 60 patients of whom the image data were available. The patients are divided as stable and unstable group by the imaging finding and clinical result. The maximum aortic dimensions, the presence of penetrating ulcer, the amount of intramural hematoma, extent of IMH were analyzed between two groups. In the follow up CT angiography, the natural courses of IMH were analyzed. Result: There were 14 type A IMHs and 46 type B IMHs. The penetrating ulcers were found in CT in 44 cases (73.3%). The most frequent location of penetrating ulcer was just distal to subclavian artery (12 cases). Out of 60 patients, 7 patients developed artic dissection, 4 patients needed emergency operation (unstable group). The rest 49 patient shows relatively stable features, even though 18 of them shows chronic lesions that need imaging follow up, such as fusiform aneurysm (n=7), conversion of penetrating ulcer to focal dissection (n=6), diffuse dilatation of aorta (n=3) and saccluar aortic aneurysm (n=2) (stable group). The type A IMH showed worse prognosis. The maximum aortic dimension shows significant difference and the presence of penetrating ulcer or amount of intramural hematoma shows no difference between stable group and unstable group. Conclusion: The ascending aorta involvement and large aortic dimension are predictor factor of progression of IMH to aortic dissection and 18.3 % (n=11/60) of all IMH developed aortic dissection or coronary involvement. The 36.7% (n= 18/49) of stable IMH developed chronic fusiform or saccluar aneurismal change.