Objective: Cardiovascular diseases are the most common cause of death in patients with renal failure. Glomerular filtration rate (GFR) is used for the assessment of the renal functional status. In this study we aimed to examine the association between severity of coronary stenosis and renal function by quantifying the coronary lesions, angiographically and calculating the renal function with the u se of GFR. Materials and Methods: Forty-three patients with decreased renal function (calculated GFR<80 ml/min) with a mean age of 67.8 ± 9.0 years and 49 patients without impaired renal function (calculated GFR≥80 ml/min) with a mean age of 52.5 ± 10.3 years were studied consecuti vely from March 2005 to September 2005. Glomerular filtration rate was calculated according to a given formula. All patients underwent selective coronary artery angiography and Gensini scoring system was used for the detection of severity of coronary atherosclerosis. Results: In linear regression analysis, a negative correlation was found between renal function and the severity of coronary atherosclerosis (r=0.326, p=0.002). All patients were classified into quartiles of Gensini score level. In multivariate analysis, the multiple-adjusted odds ratio (OR) of the risk of decreased renal function was 0.99 (95% CI 0.24-4.15) for quartile 2, 4.38 (95% CI 1.11-17.20, p =0.03) for quartile 3, and 7.01 (95% CI 1.72-28.61, p=0.007) for quartile 4 of Gensini score level compared with the quartile 1. Conclusion: Coronary atherosclerosis quantified by Gensini score is significantly associated with the severity of decreased renal function and this association is independent of age and other cardiovascular risk factors.