BACKGROUND Ezetimibe, a first-in-its-class inhibitor of cholesterol absorption, is an effective agent for combined use with statins to achieve low-density lipoprotein cholesterol (LDL-C) goals. Ezetimibe in combination with simvastatin as a single-tablet formulation has proven to be highly effective in reducing serum LDL-C through the dual inhibition of cholesterol absorption and biosynthesis. The effect of time of administration on efficacy of this combination therapy has not been evaluated. OBJECTIVE To compare the effects of morning versus evening administration of ezetimibe/simvastatin on serum cholesterol levels of patients with primary hypercholesterolemia. METHODS In this multicenter, open-label, randomized, 2-sequence, 2-period crossover study, patients with primary hypercholesterolemia randomly received ezetimibe/simvastatin 10 mg/20 mg once daily, either in the morning (within 1 hour of breakfast) or in the evening (within 1 hour of dinner) for 6 weeks. RESULTS Data on 171 patients (87 in the morning administration group and 84 in the evening administration group) were analyzed. A significant reduction (p ≤ 0.001) in the total cholesterol, triglyceride, high-density lipoprotein cholesterol, LDL-C, apo-lipoprotein B, and high-sensitivity C-reactive protein (hs-CRP) from baseline was achieved after each treatment. Noninferiority of morning administration versus evening administration was shown in the percentage reduction of the LDL-C level from baseline (difference, -1.62%; 90% CI -4.94 to 1.70). No significant difference was found between groups with respect to the percentage of changes in other lipid parameters from baseline. Furthermore, there was no significant difference in the percentage of change in hs-CRP as an antiinflammatory marker between the morning and evening administration groups. The frequency of adverse events was similar between groups. CONCLUSIONS Morning administration of ezetimibe/simvastatin 10 mg/20 mg is noninferior to evening administration with respect to LDL-C- lowering ability.