Background Although the anti-atherosclerotic effects of HMG-CoA reductase inhibitors are well known, their specific effect on saphenous vein grafts after coronary artery bypass graft (CABG) operation is not well documented and has not been studied in Japan, so the aim of the present prospective randomized controlled study involving 27 Japanese institutions was to investigate the effects of pravastatin on the progression of atherosclerosis in such grafts and native coronary arteries after CABG. Methods and Results A total of 303 patients who had undergone CABG were randomly assigned to either the pravastatin group (n=168) or the control group (n=167). Paired coronary angiograms were obtained at baseline and at the end of 5-year follow-up in 182 (60%) patients. The low-density lipoprotein cholesterol concentration significantly decreased in the pravastatin group from 141.4 mg/dl to 113.7 mg/dl (-19.6%), compared with 141.1 mg/dl to 133.7 mg/dl (-5.2%) in the control group (p<0.001). Although there was no significant difference in the quantitative coronary angiography measurements between the 2 groups, the global change score indicated a significant pravastatin-mediated reduction in plaque progression (p<0.01). Conclusions Pravastatin can potentially reduce atherosclerotic progression in both the bypass graft and native coronary arteries of patients after CABG. (Circ J 2005; 69: 636 - 643)