We reported previously that 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (RIs) suppressed in vitro oxidized-low density lipoprotein-induced macrophage growth. To elucidate whether HMG-CoA RIs have anti-atherogenic effects separate from their cholesterol-lowering effect, total plasma levels of cholesterol in patients with type 2 diabetes mellitus (type 2 DM) and hypercholesterolemia were reduced to normal by one-year treatment with HMG-CoA RIs and intimal-medial thickness (IMT) of the common carotid arteries (CCA) was measured. Patients with type 2 DM and hypercholesterolemia received either pravastatin (n = 15) or simvastatin (n = 15), while another group of type 2 DM patients with normocholesterolemia did not receive these agents. IMT of the CCA was measured using Powervision SSA-370A, probe 7.5 Mhz. The mean IMT and the rate of increase of IMT were relatively elevated in the order of the simvastatin-treatment group, pravastatin-treatment group, and control group. Our results suggested that HMG-CoA RIs might have anti-atherogenic effects in addition to their cholesterol-lowering effect. J Atheroscler Thromb, 2005; 12: 149-153.