OBJECTIVE: This study investigated levels of interleukin (IL)-34, a proinflammatory cytokine, in patients with coronary artery disease (CAD). METHODS: Following coronary artery angiography, 91 patients with CAD (including stable and unstable angina pectoris) were divided into two groups, the CAD group (coronary artery stenosis ≥ 50%) and the control group (coronary artery stenosis < 50%). Serum levels of factors including IL-34 and high sensitivity C-reactive protein (hs-CRP) were measured. RESULTS: IL-34 and hs-CRP levels were significantly higher in the CAD group than in the control group (191.3 ± 17.9 pg/ml versus 125.4 ± 14.8 pg/ml and 3.08 ± 1.81 mg/ml versus 1.42 ± 1.01 mg/ml, respectively), with a significantly positive correlation between IL-34 and hs-CRP levels in the CAD group. Multiple regression analysis showed that IL-34 and hs-CRP levels were independent predictors of CAD (IL-34: odds ratio [OR] 2.073, 95% confidence intervals (CI) 1.419, 2.672; hs-CRP: OR 1.878, 95% CI 1.172, 2.531). CONCLUSIONS: IL-34 levels were significantly increased in patients with CAD, and positively correlated with hs-CRP levels, suggesting that IL-34 may be an independent predictor of CAD.