We assessed the relationship between the severity of coronary artery disease assessed by SYNTAX score (SS) and neutrophil to lymphocyte ratio (N:L ratio) in patients with ST elevation myocardial infarction (STEMI). In total, 840 patients with STEMI in whom primary percutaneous coronary intervention was performed were prospectively included (622 male, 218 female; mean age 58.6 ± 12.4 years). Total and differential leukocyte counts and other biochemical markers were measured at admission. Patients were categorized into tertiles on the basis of SS. The N:L ratio of SShigh group was higher compared with SSlow and SSmid groups (P <.001 for all). Multivariate regression analysis showed that N:L ratio (β =.277, P <.001), ejection fraction (β = -.086, P =.012), age (β =.104, P =.004), and diabetes (β =.152, P <.001) were the independent predictors for SS in patients with STEMI.