Background It is unclear whether a marked reduction of low-density lipoprotein-cholesterol (LDL-C) in patients with coronary heart disease (CHD) and mild hypercholesterolemia leads to less progression of atherosclerosis. Methods and Results Patients with CHD and hypercholesterolemia (100<LDL-C <140 mg/dl) who underwent coronary angiography (CAG) and intravascular ultrasound (IVUS) were randomly assigned to the atorvastatin (10-20 mg/day) group or `usual care' group. After 12 months 58 patients had follow-up CAG and IVUS studies that could be evaluated. Cross-sectional areas of the vessel, lumen, and plaque were measured at 1-mm intervals, and volumetric calculations were based on Simpson's rule. After 12 months, the mean reduction of LDL-C was 34% in the atorvastatin group and 0% in the usual care group (p<0.01). The mean absolute plaque volume showed a larger increase in the usual care group than in the atorvastatin group (atorvastatin -1.4±11.6 mm³, usual care 7.6±10.3 mm³; p<0.01). Vessel volume also showed a larger increase in the usual care group than in the atorvastatin group (atorvastatin 2.2±10.9 mm³, usual care 10.9±17.7 mm³; p=0.03). Conclusions Atorvastatin treatment prevented the further progression of atherosclerosis by maintaining LDL-C below 100 mg/dl in patients with CHD and hypercholesterolemia (100<LDL-C <140 mg/dl). (Circ J 2007; 71: 1845 - 1850)