Background: Long-term natural history of the distal aortic dissection (AD) and predictors of the late aneurysmal change have yet to be demonstrated. Methods: Contrast-enhanced computed tomography (CT) was performed during the acute phase in 100 patients including 49 patients with type 3 AD and 51 with type 1 AD. All patients with type 1 AD received ascending aorta graft replacement. Clinical observation was conducted for 53짹26 months, and CT was repeated after 31짹27 months in 97 patients. Aorta diameters and false lumen diameters were measured in upper (UT), mid (MT) and lower descending thoracic (LT), and abdominal aorta (AA). Results: Average rates of diameter dilatation in UT, MT, LT and AA were 0.19, 0.19, 0.17, and 0.09 mm/month, respectively. These rates were not different between type 1 and 3 AD. Aneurysmal change (diameter ��� 60 mm) occurred in 14.4, 8.2, 4.1, and 3.1% of patients at UT, MT, LT and AA, respectively. Among 53 patients in whom CT was repeated after ��� 2 years, aneurysmal change was developed in 15 patients (28%). The false lumen diameter at UT (p<0.005), aorta diameter at MT (p<0.05) in the acute phase CT and Marfan syndrome (p<0.05) were independent predictors of the late aneurysmal change by multiple logistic regression analysis. False lumen diameter at UT ��� 22 mm in the initial CT predicted late aneurysmal change with sensitivity 100% and specificity 76%. The patients with initial false lumen diameter at UT ��� 22 mm (n=42) showed higher event rate (aneurysmal change or death) than others (n=58) (p<0.001). Conclusion: UT is the major site of late aneurysmal change. A large false lumen diameter at UT in the initial CT portends late adverse outcome warranting early intervention.