Objectives: The aim of this study was to assess the feasibility of aortic diameter as a current criterion for elective aortic surgery to prevent the development of aortic dissection in non-Marfan and Marfan (MFS) patients. Background: Among the parameters considered during watchful follow-up for the genesis of acute type A aortic dissection, aortic size has been considered a cardinal factor. Preventive surgery of the aorta in asymptomatic patients on the basis of size alone is still controversial in patient populations lacking risk factors for aortic dissection. Methods: We reviewed the data for patients diagnosed with acute type A aortic dissection from December 1994 to March 2009 at our institute. Results: A total of 237 patients who presented with acute type A aortic dissection were enrolled, of which 31 were diagnosed with MFS. The maximal ascending aorta size was 46.7 mm (42.9 mm–51.6 mm) in non-MFS patients and 58.5 mm (43.8 mm–64.9 mm) in MFS patients (p < 0.001). Two-thirds (74.1%) of MFS patients had a maximal aortic root size ��� 45 mm. However, 86.9% of the 206 non-MFS patients had aortic diameters < 55 mm. Non-MFS patients presenting with an aortic size < 55 mm developed aortic dissection at a younger age and had a higher body mass index than those with aortic sizes ��� 55 mm. Conclusion: Aortic diameter is of limited value and is not a critical parameter for aortic dissection in non-MFS patients.