Background The cardiovascular event rate in Japanese populations is strikingly lower than that in Caucasian populations and it has been postulated that this difference might be because of variations in atherosclerosis progression in patients with coronary artery disease (CAD). However, the rate of angiographically assessed progression and its response to statins has not been well described in Japanese patients. Methods and Results The angiographic intervention trial using an HMG-CoA reductase inhibitor to evaluate the retardation of obstructive multiple atheroma (ATHEROMA) study was a multicenter, randomized, controlled clinical trial investigating the effects of pravastatin on coronary atherosclerosis in Japanese patients with CAD using quantitative coronary angiography. In total, 361 patients with mild to moderate elevated serum total cholesterol concentrations (195-265 mg/dl) received diet only (n=179) or diet plus pravastatin 10-20 mg/dl (n=182). Over 3 years, low-density lipoprotein-cholesterol in the pravastatin group decreased by 19.5% (p<0.0001). A per-patient analysis showed that minimum lumen diameter increased by 0.034±0.17 mm in the pravastatin group, but decreased by 0.006±0.16 mm in the diet only group (p=0.04). The mean difference between the treatment groups was 0.040 mm (95% confidence interval 0.020, 0.070 mm). Conclusion The ATHEROMA study indicates that pravastatin 10-20 mg/day for 3 years improves hyperlipidemia, then suppresses progression and induces regression of focal coronary atherosclerosis in Japanese CAD patients with elevated serum cholesterol. (Circ J 2005; 69: 875 - 883)