Background: We intended to outline the pathological changes and the etiology of the ascending aortic dilatation, based on the histopathological findings in patients who received the replacement of the dilated ascending aorta. Methods: Ascending aortic replacement was accomplished in 24 (16 male, 8 female, mean age 57.5 ± 8.5) consecutive patients in our center. Mean measured, predicted aortic diameters and aortic ratio were found 5.0 ± 0.5 cm, 2.8 ± 0.1 cm, 1.8 ± 0.2 respectively. Hypothermic cardiopulmonary bypass (mean 224 ± 82 min.), cardioplegic arrest (mean 106 ± 59 min.) and deep hypothermic circulatory arrest (22 patients, mean 19.9 ± 4.8 min.) were utilized. Concomitant cardiac procedures were performed in 21 patients. Histopathological examination of the aortic specimen was performed in 23 patients. Results: Medial degeneration (n = 14) or atherosclerotic degeneration (n = 9) was observed in histopathological examination. Age, gender, aortic diameter, aortic ratio, history of smoking, presence of hypertension and bicuspid aortic valve were compared between the patients falling into two histopathological definitions. These demographic and clinical data did not differ significantly. Cardiovascular diseases were not significantly different between the patients with either of these pathologies. Conclusion: Dilated ascending aorta is associated with medial degeneration or atherosclerotic degeneration of the aortic wall. Clinical and demographic characteristics of patients having these pathologies are not different. Both pathologies can be observed with isolated dilatation of the ascending aorta or with dilatation of the ascending aorta associated with aortic valve and/or coronary heart disease.