The SYNTAX score (SXscore) is an anatomic scoring system based on coronary angiography (CA) that not only quantifies lesion severity and complexity but also predicts poor cardiovascular outcomes, including mortality, in patients with acute coronary syndromes (ACS). Recent studies have shown that platelet-to-lymphocyte ratio (PLR) is associated with worse outcomes in many cardiovascular diseases. The aim of this study was to investigate the association of PLR with the severity and complexity of coronary atherosclerosis as assessed by the SXscore in patients with ACS who underwent urgent CA. A total of 1,016 patients with ACS who underwent urgent CA were included in the study from August 2012 to March 2014. Admission PLR values were calculated before CA was performed. The SXscore was determined from baseline CA. The patients were divided into 2 groups, those with low SXscores (<= 22) and those with intermediate to high SXscores (>= 23). PLRs were significantly higher in patients with intermediate to high SXscores compared with those with low SXscores (p <0.001). In-hospital mortality was significantly higher in the groups with high PLR and intermediate to high SXscores. In multivariate analysis, the independent predictors of intermediate to high SXscore were PLR (odds ratio 1.018, 95% confidence interval 1.013 to 1.023, p <0.001) together with the left ventricular ejection fraction (odds ratio 0.935, 95% confidence interval 0.910 to 0.960, p <0.001), and age (odds ratio 1.029, 95% confidence interval 1.029 to 1.054, p = 0.02). A PLR >= 116 had 71% sensitivity and 66% specificity in predicting intermediate to high SXscore. In conclusion, the PLR at admission is significantly associated with the severity and complexity of coronary atherosclerosis in patients with ACS. Increased PLR is an independent predictor of higher SXscore in patients with ACS who undergo urgent CA. (C) 2014 Elsevier Inc. All rights reserved.