Objectives: The prognostic importance of red cell distribution width (RDW) and neutrophil/lymphocyte ratio (NLR) in cardio- vascular diseases has been shown. Ascending aortic dilata- tion (AAD) is a common cardiovascular disease and is associ- ated with aortic wall inflammation and cystic degeneration. In this study, we aimed to investigate the relationship between serum levels of RDW, NLR and the presence of AAD. Study design: Two-hundred consecutive patients with AAD diagnosed by transthoracic echocardiography were pro- spectively recruited and were compared to 170 age-gender- matched subjects with normal aortic diameters. Complete blood counts (CBCs) were analyzed for hemoglobin, RDW and NLR counts, as well as mean corpuscular volume (MCV). If possible, results of CBC tests within the previous two years were also included and the averages were used. Results: RDW [median 13.9, interquartile range (IQR) 1.40 vs. median 13.3, IQR 1.05%, p=0.01], NLR (median 2.04, IQR 1.09 vs. median 1.78, IQR 0.90, p=0.01) and high-sensitive C- reactive protein (hs-CRP) (median 0.60, IQR 0.80 vs. median 0.44, IQR 0.68 mg/L, p=0.01) levels were significantly higher in the AAD group compared to the control group. In univariate correlation analysis, ascending aortic diameters were corre- lated with RDW levels (r=0.31, p=0.01), NLR levels (r=0.15, p=0.01) and hs-CRP levels (r=0.12, p=0.03). In multivariate logistic regression analysis, increased levels of RDW and hs- CRP remained as the independent correlates of AAD in the study population. Receiver operating characteristic (ROC) curve analysis revealed that a RDW measurement higher than >13.8% predicted AAD with a sensitivity of 49.5% and a speci- ficity of 82.8% (area under the curve [AUC] 0.681, p=0.01). Conclusion: In patients with AAD, RDW and hs-CRP levels are increased, which may indicate the role of inflammation in the pathogenesis of AAD.