This study compared the efficacy and safety of co-administered ezetimibe + simvastatin with atorvastatin monotherapy in adults with hypercholesterolemia. Seven hundred eighty-eight patients were randomized 1:1:1 to 3 treatment groups; each group was force-titrated over four 6-week treatment periods: (1) 10 mg of atorvastatin as the initial dose was titrated to 20, 40, and 80 mg; (2) co-administration of 10 mg of ezetimibe and 10 mg of simvastatin (10/10 mg) was titrated to 10/20, 10/40, and 10/80 mg of ezetimibe + simvastatin; and (3) co-administration of 10/20 mg of ezetimibe + simvastatin was titrated to 10/40 mg (for 2 treatment periods) and 10/80 mg of ezetimibe + simvastatin. Key efficacy measures included percent changes in low-density lipoprotein cholesterol (LDL) and high-density lipoprotein cholesterol (HDL) from baseline to the ends of (1) treatment periods 1 and 2 (for LDL cholesterol) comparing co-administration of 10/20 mg and 10/10 mg of ezetimibe + simvastatin with 10 mg of atorvastatin and (2) treatment period 4 (for LDL cholesterol and HDL cholesterol) comparing co-administration of 10/80 mg of ezetimibe + simvastatin with 80 mg of atorvastatin. Baseline LDL and HDL cholesterol levels were comparable between treatment groups. At the end of treatment period 1, the mean decrease of LDL cholesterol was significantly (p </=0.001) greater for co-administration of 10/10 mg and 10/20 mg of ezetimibe + simvastatin than for 10 mg of atorvastatin. At the end of treatment period 4 and after comparing maximum doses, co-administration of 10/80 mg of ezetimibe + simvastatin was superior to 80 mg of atorvastatin in the percent LDL cholesterol decrease (-59.4% vs -52.5%, p <0.001) and HDL cholesterol increase (12.3% vs 6.5%; p <0.001). All treatments were well tolerated. Thus, a greater LDL cholesterol decrease and HDL cholesterol increase were attained by treating patients with co-administration of ezetimibe and simvastatin than with atorvastatin.