BACKGROUND Inflammation plays a key role in atherosclerosis, and discovering new biomarkers of inflammation is becoming important in order to uncover the pathogenesis of atherosclerotic coronary artery disease (CAD). Recent studies have focused on polymorphonuclear neutrophils. It has been suggested that human neutrophil peptide 1-3 (HNP1-3) is proatherogenic. In this study, we aimed to investigate the associations between plasma HNP1-3 levels and the severity of atherosclerosis via a generally accepted scoring system. METHODS This cross-sectional, observational study included 107 consecutive patients suffering from stable angina pectoris and undergoing coronary angiography (CAG). Patients were divided into two groups according to the Gensini scoring (GS) system evaluating disease severity. Group 1 was composed of mild CAD patients with GS < 20 and group 2 consisted of severe CAD patients with GS ≥ 20. Plasma HNP1-3 levels were assessed by the ELISA method. RESULTS The mean HNP1-3 levels were found to be lower in group 1 than group 2 (134.7 ng/ml vs. 147.5 ng/ml). HNP1-3 levels were significantly higher in the severe CAD group than the mild CAD group according to GS (p < 0.001). The results of multivariate logistic regression analysis revealed that only age > 62 years and HNP1-3 > 134 ng/ml were independent predictors of the severity of CAD after adjusting for gender, smoking, hypertension, hyperlipidemia, diabetes, family history of CAD and white blood cell count. In predicting the severity of CAD, the sensitivity and specificity of HNP1-3 were 83.9% (p < 0.001) and 58.8% (p < 0.001), respectively. CONCLUSIONS This study revealed that the plasma levels of HNP1-3 were significantly higher in severe CAD than mild CAD.