BACKGROUND; AAS is mainly developed in 40 - 70 years with typical presentation. AAS in young patients (���40 years) or elderly patients (���70 years) might have unique clinical characteristics, management, and outcomes. The aim of this study was to analyze the clinical differences according to the age. METHODS; Data were collected on 483 patients diagnosed with AAS between January 1995 and February 2009. Among total patients with AAS, two categories of patients, ��� 40 years of age (the young group) and ��� 70 years (the elderly group), were compared. To investigate the differences in two groups, we analyzed baseline characteristics, clinical presentation, CT findings, management, complication and prognosis during follow-up. RESULTS; Sixty-six patients (14%) with AAS belonged to the young group and 93 patients (19%) to the elderly group. Compared with the elderly group, the young group demonstrated a higher incidence of aortic dissection (98.5% vs. 60 %, p<0.001), lower incidence of intramural hematoma (1.5% vs. 40 %, p<0.001), predominance of male (83.3% vs. 37.6%, p<0.001), and higher prevalence of Marfan syndrome (27.3% vs. 0%, p<0.001). Clinical symptoms at presentation were similar in two groups, however, syncope (0% vs.12.9%, p=0.001) and hypotension (4.5% vs. 16.1%, p =0.023) were significantly more common in the elderly group than in the young group. The extension of AAS to the iliac artery was more common in the young group (61.1% vs. 21.3%, p<0.001). The in-hospital mortality was similar in both groups (3% vs. 9.7 %, p=0.124). Of the 124 patients who underwent imaging follow-up for ��� 1 month, the young group showed more aortic dilatation (���2 cm) at the upper level of the descending thoracic aorta (9.6% vs. 0%, p=0.012) and the mid level of the descending thoracic aorta (11.5% vs. 1.4%, p=0.021) between initial and follow-up CT(mean follow-up duration 33짹40 month vs 20짹26 month). Therefore, the young group was more likely to undergo operation of the distal aorta due to dilatation of the descending aorta. Especially, Marfan syndrome was significantly associated with operation of the distal aorta during follow-up. CONCLUSION; Our study shows significant differences between younger and elderly patients with AAS in their clinical characteristics, management, and prognosis. These differences will help to understand potentially age-related differences among patients with AAS.