OBJECTIVE: We investigated whether the inflammatory biomarker YKL-40 could improve the long-term prediction of death made by common risk factors plus high-sensitivity C-reactive protein (hs-CRP) and N-terminal-pro-B natriuretic peptide (NT-proBNP) in patients with stable coronary artery disease (CAD). BACKGROUND: Non-hospitalized CAD patients are usually followed in general practice. There is a need for identify biomarkers which could help to foresee the prognoses of these patients. Elevated serum YKL-40 is a short-term predictor for myocardial infarction, cardiovascular mortality and all-cause mortality in patients with stable CAD. METHODS: Serum YKL-40, hs-CRP, and NT-proBNP were measured in 4265 (97.6%) of the 4372 patients with stable CAD included in the CLARICOR trial, and death was registered in a 6-years follow-up period. RESULTS: The median serum YKL-40 was 110 μg/L [IQR=93], hs-CRP 2.8 mg/L [IQR=4.74], and NT-proBNP 203 ng/L [IQR=407]. During 6 years follow-up period 923 (21.1%) patients died. After adjustment for type of intervention, risk factors (age, sex, hypertension, diabetes, smoking status, and previous myocardial infarction) and medical treatment (diuretics, digoxin, and statin) serum YKL-40 (transformed as ln(max(82, YKL-40/μg/L)) was significantly associated with all-cause mortality [hazard ratio (HR)=1.55, 95% CI=1.39-1.73, p<0.001]. After additional adjustment for ln(hs-CRP) and ln(NT-proBNP) this was still true [HR=1.38, 95% CI=1.21-1.53, p<0.001]. CONCLUSIONS: Serum YKL-40 is a predictor of long-term mortality in patients with stable CAD independent of common risk factors and ln(hs-CRP) and ln(NT-proBNP). Serum YKL-40 can be used for prognostication in these patients.