['The aim of this study was to assess whether NLR levels are associated with echocardiographic parameters, New York Heart Association (NYHA) functional class, or B- type natriuretic peptide (BNP) levels in patients with idiopathic dilated cardiomyopathy (DCM).', 'Eighty-seven patients with idiopathic DCM were included prospectively from 2009 to 2014. Patients with acute decompensated heart failure and conditions that alter the total or differential white blood cell counts were excluded. Blood samples were collected before echocardiographic investigation on admission.', 'There was a statistically significant correlation between neutrophil/lymphocyte ratio (NLR) and NYHA functional class (r = 0.68, p < 0.001), BNP levels (r = 0.61, p < 0.001) and various echocardiographic parameters. NLR was significantly higher in patients in NYHA functional class III or IV (n = 39) than among those categorized as NYHA class I or II (n = 48), (3.3 ± 1.0 vs 2.1 ± 0.6; p < 0.001). The NLR cutoff value predicting severe chronic HF was 2.25 with 82% sensitivity and 65% specificity (p < 0.001). On multivariate linear regression analysis NLR (p = 0.025), left ventricular end-diastolic volume (p = 0.041) and left atrial volume index (LAVI) (p = 0.001) were found to be independent positive predictors of BNP levels.'] Is neutrophil/lymphocyte ratio related to the severity of idiopathic dilated cardiomyopathy?