Objective: The purpose of this study was to determine normal reference values of intra-thoracic and abdominal aortic diameters of asymptomatic Thai adults obtained by multidetector computed tomography. Secondary end points were evaluation of relationships between aortic diameters and patients’ demographic data or potential risk factors of cardiovascular disease. Methods: Three hundred and ten Thai adults in Siriraj Hospital who had no any signs or symptoms of cardio- vascular disease that examined with computed tomography (CT) of chest and whole abdomen were investigated in this study. Aortic diameters were measured at eight predefined intra-thoracic and abdominal levels on CT images, including ascending aorta, proximal transverse aortic arch, distal transverse aortic arch, aortic isthmus, thoracoabdominal junction, celiac axis, suprarenal aorta and aortic bifurcation. Analysis of data was performed with regard to patients’ demographic data (age, sex, weight, and height) and three potential risk factors of cardio- vascular disease (hypertension, dyslipidemia and diabetes mellitus). Furthermore, we also recorded the co-morbid non-cardiovascular underlying diseases which were classified into seven groups, including tumors (malignant and benign tumors), infectious diseases, inflammatory diseases, autoimmune diseases, degenerative diseases, psychiatric diseases and others. Results: Aortic diameters were 3.14±0.40 cm. at the ascending aorta, 2.88 ± 0.34 cm. at proximal transverse aortic arch, 2.65±0.30 cm. at distal transverse aortic arch, 2.46 ± 0.31cm. at aortic isthmus, 2.10± 0.27 cm. at thoracoab- dominal junction, 1.99 ± 0.26 cm. at celiac axis, 1.81 ±0.25 cm. at suprarenal aorta, and 1.47±0.21 cm. at aortic bifurcation. Overall aortic diameters tend to continuously significantly decrease aortic diameters from proximal to distal direction from ascending aorta to aortic bifurcation. Men had slightly more enlarged aortic diameters in all eight predefined levels than women with statistical significance (p