Background: An enlargement of the aortic diameter exceeding at least 50% of the normal range results in aneurysm formation. Endovascular stent grafting is a newer form of treatment for thoracic aortic aneurysms that is less invasive than open surgery and has the success rate around 95%. The ratio of stent graft size to aortic diameter should be of the order of 1.1__ampersandsignndash;1.15; higher diameters have to be avoided in order to limit the vessel wall stretch which may result in antegrade or retrograde dissection or perforation. After reviewing the literature thoroughly, it was found that even though the diameter of ascending and descending aorta has a wide range of clinical implications and applications, there is dearth of literature pertaining to the quantitative measurements of the diameters of ascending and descending aorta in Indian subjects. Aim: __ampersandsignbull; To measure the diameter of ascending aorta (DOAA) and diameter of descending aorta (DODA) at the level of pulmonary artery bifurcation in Indian subjects using computed tomography. __ampersandsignbull; To establish the upper normal limits of DOAA and DODA; to rule out aneurysm of thoracic aorta. Materials and Method: The CT chest images of 76 patients (44 males and 32 females) were studied. The DOAA and DODA were measured at the level of pulmonary artery bifurcation; across a line joining the ascending and the descending aorta. Results: 1. The average DOAA was 33.44 mm __ampersandsignplusmn; 1.12 mm in males and 31.43 mm __ampersandsignplusmn; 1.52 mm in females; the upper normal limits of DOAA were 35.68 mm for males and 34.47 mm for females. 2. The average DODA was 25.11 mm __ampersandsignplusmn; 1.34 mm in males and 23.04 mm __ampersandsignplusmn; 1.58 mm in females; the upper normal limits of DODA were 27.79 for males and 26.20 for females. Conclusion: A quantitative assessment of the diameters of ascending and descending aorta has been presented which will help the clinicians for diagnostic and therapeutic purpose especially in Indian subjects.__ampersandsignnbsp;