We investigated, in a prospective study of 1,007 patients who underwent coronary angiography for suspected coronary artery disease (CAD), the association of obstructive CAD with severe or moderate decrease in glomerular filtration rate (GFR) calculated from the Modification of Diet in Renal Disease equation. Baseline characteristics were similar in patients with a moderate or severe GFR decrease (<60 ml/min/1.73 m(2)) and those with a mild or no GFR decrease except for diabetes being present in 112 of 259 patients (43%) with a moderate or severe GFR decrease and in 206 of 748 patients (28%) with a mild or no GFR decrease (p <0.001). Three-vessel CAD was present in 138 of 259 patients (53%) with a moderate or severe GFR decrease and in 170 of 748 patients (23%) with a mild or no GFR decrease (p <0.001). One- to 3-vessel CAD was present in 225 of 259 patients (87%) with a moderate or severe GFR decrease and in 533 of 748 patients (71%) with a mild or no decrease in GFR (p <0.001). Logistic regression analysis showed that patients with a moderate or severe GFR decrease had a 4.1 times higher risk of developing 3-vessel CAD after controlling for the effect of diabetes compared with patients with a mild or no GFR decrease (relative risk 4.1, 95% confidence interval 3.0 to 5.5). In conclusion, a moderate or severe decrease in GFR is a significant risk factor for 1- to 3-vessel obstructive CAD, especially 3-vessel obstructive CAD.