We aimed to elucidate the relationship between mild to moderate renal impairements and burden of atherosclerosis in patients with acute coronary syndrome (ACS). A total of 380 patients with ACS were included in the study. Gensini and SYNTAX scores were also calculated. Kidney function was classified based on estimated glomerular filtration rate (eGFR) into stage 1: eGFR > 90, stage 2: 60 to 89, and stage 3: 30 to 60 mL/min per 1.73 m(2). Gensini and SYNTAX scores were higher in stages 2 and 3 than in stage 1. Also, the number of diseased vessels, number of critical lesions (> 50 and 70%), left main disease, and number of total occlusion vessels were higher in stages 2 and 3 than in stage 1. Multivariate linear regression analysis demonstrated that a decreased eGFR was an independent risk factor for SYNTAX and Gensini scores together with age and male gender.