This study was designed to evaluate the effects of lipid-lowering therapy by atorvastatin versus simvastatin on calcified plaque progression, as determined by serial electron beam tomography (EBT), in primary prevention patients. In this observational study, serial EBT was performed before and after 1.2 years of atorvastatin (n = 103) and simavastatin therapy (n = 46); approximately 50% of each group was on niacin as well, in similar doses. There were no differences in demographic parameters between the groups. Total, low-density lipoprotein (LDL), and non-high-density lipoprotein (HDL) cholesterol were significantly higher in the atorvastatin group before treatment. Before treatment, EBT calcium score and volume scores were 469 and 378, respectively, in the atorvastatin patients, and 388 and 307, respectively, in the simvastatin patients (p = NS, atorvastatin vs simvastatin). After treatment, there were no differences in any lipid or EBT values between the groups. Post-treatment total cholesterol and LDL cholesterol were 156 and 79 mg/dl, respectively, in the atorvastatin cohort and 154 and 76 mg/dl, respectively, in the simvastatin group (p = NS). Calcium score and volume progressed 10.8%/year and 8.5%/year, respectively, in the atorvastatin group, and 7.5%/year and 7.8%/year in the simvastatin group (p = NS, atorvastatin vs simvastatin). We conclude that aggressive treatment with atorvastatin and simvastatin in the primary prevention population, to similar lipid levels, is associated with equal progression of EBT-determined calcified plaque. This suggests that these hydroxymethylglutaryl coenzyme A reductase inhibitors exhibit a "class effect" with respect to progression of subclinical atherosclerosis.