Background : Osteoprotegerin(OPG) is a glycoprotein that acts by competing with receptor activator of nuclear factor-kB(RANK) for binding RANK ligand(RANKL) and plays a critical role in bone remodeling. Recently, OPG has been reported to be associated with cardiovascular disease. The aim of this study is to investigate the relation between plasma OPG level and conventional cardiovascular risk factors in patients with definite coronary artery disease(CAD). Methods: In 583 consecutive patients(mean age: 62짹10yrs, M:F=398:185) underwent percutaneous coronary intervention(PCI) in St Mary���s hospital from April 2003 to February 2005, plasma OPG levels were determined at the time of coronary angiogram. Baseline clinical and laboratory data including HbA1c and hsCRP were obtained at the day of admission. Intima media thickness(IMT) of common carotid artery were also assessed among 252 patients. Results: 1. Plasma OPG level was correlated with IMT(r=0.184, p=0.003) and median plasma OPG level was elevated in accordance with the severity of CAD(2704 in 1VD vs 2914 in 2VD vs 3046pg/ml in 3VD, p=0.024). 2. Median plasma OPG levels were significantly higher in female(3024 vs 2828 pg/ml, p=0.003) and DM patients(3098 vs 2711 pg/ml, p<0.001) but not in hypertensive patients. 3. Plasma OPG level was positively correlated with age(r=0.340, p<0.001), fasting glucose(r=0.129,p=0.002) and HbA1C level(r=0.102, p=0.035) but showed inverse correlation with BMI(r=-0.199, p<0.001). 4. Plasma OPG level was not correlated with lipid profile and hsCRP. 5. By multivariate logistic regression analysis, increasing age(odds ratio 1.053[95% confidence interval, 1.034-1.073]), DM(odds ratio 1.664[95% confidence interval, 1.149-2.410]), lower BMI less than 25kg/mm²(odds ratio, 1.625 [95% confidence interval,1.142-2.314])was associated with supramedian OPG level(2831pg/ml) but association of female gender disappeared. Conclusion : Plasma OPG level has close relation with the severity of CAD, carotid atherosclerosis, and also with well known cardiovascular risk factors especially DM and age. It might suggest the role of OPG as a biochemical marker of atherosclerosis.