Background: Studies have demonstrated a consistent relationship between white blood cell (WBC) counts and coronary artery disease (CAD). The neutrophil/lymphocyte ratio (NLR) has been considered as a potential marker for identifying individuals under risk of CAD and associated events. In this study, we aimed to evaluate whether NLR was associated with the severity and morphology of coronary atherosclerotic plaques shown by multidetector computed tomography (MDCT). Methods: Our study population consisted of 684 patients who underwent dual-source 64 slice MDCT for the assessment of CAD. Coronary arteries were evaluated on a 16-segment basis and critical coronary plaque was described as luminal narrowing > 50%, whereas plaque morphology was assessed on a per segment basis. Total WBC, neutrophil and lymphocyte counts were determined using commercially available assay kits. Results: WBC count [7700 (6400-8800) vs. 6800 (5700-7900), p < 0.05] and NLR [2.40 (1.98-3.07) vs. 1.86 (1.50- 2.38), p < 0.001] were found to be higher in patients with critical stenosis than in those without. In the binary logistic regression analysis, NLR was a predictor of critical stenosis (odds ratio, 1.68; 95% confidence interval, 1.39-2.03, p < 0.001). NLR levels differed among plaque morphology subtypes (p < 0.05) and was significantly higher in non-calcified plaque (NCP) compared to mixed plaque (MP) and calcified plaque (CP) (p < 0.05). In the multinomial logistic regression analysis, NLR was found to be an independent predictor of NCP,MP and CP (p < 0.001). Conclusions: These data show that NLR is associated with both the severity and morphology of coronary atherosclerotic disease.