Objective: To compare the efficacy and safety of 10 mg of ezetimibe coadministered with simvastatin with the safety and efficacy of simvastatin monotherapy for patients with hypercholesterolemia. Patients and Methods: This multicenter double-blind, placebo-controlled, factorial study enrolled 887 patients with hypercholesterolemia (low-density lipoprotein cholesterol [LDL-C], 145-250 mg/dL; triglycerides, ≤350 mg/ dL). Patients were randomized to 1 of 10 treatments-placebo, ezetimibe at 10 mg/d, simvastatin at 10, 20, 40, or 80 mg/d, or simvastatin at 10, 20, 40, or 80 mg/d plus ezetimibe at 10 mg/d for 12 weeks. The study began March 13,2001, and ended January 8, 2002. The primary efficacy end point was the mean percent change in LDL-C levels from baseline to study end point (last available postbaseline LDL-C measurement) for the pooled ezetimibe/simvastatin group vs the pooled simvastatin monotherapy group. Results: Coadministration of ezetimibe/simvastatin was significantly (P<.001) more effective than simvastatin alone in reducing LDL-C levels for the pooled ezetimibe/ simvastatin vs pooled simvastatin analysis and at each specific dose comparison. The decrease in LDL-C levels with coadministration of ezetimibe and the lowest dose of simvastatin, 10 mg, was similar to the decrease with the maximum dose of simvastatin, 80 mg. A significantly (P<.001) greater proportion of patients in the ezetimibe/ simvastatin group achieved target LDL-C levels compared with those in the monotherapy group. Treatment with ezetimibe/simvastatin also led to greater reductions in total cholesterol, triglyceride, non-high-density lipoprotein cholesterol, and apolipoprotein B levels compared with simvastatin alone; both treatments increased high-density lipoprotein cholesterol levels similarly. The safety and tolerability profiles for the ezetimibe/simvastatin and monotherapy groups were similar. Conclusion: Through dual inhibition of cholesterol absorption and synthesis, coadministration of ezetimibe/ simvastatin offers a highly efficacious and well-tolerated lipid-lowering strategy for treating patients with primary hypercholesterolemia.