["Ezetimibe as monotherapy or in combination with statins effectively lowers low-density lipoprotein cholesterol (LDL-C). However, there are few reports of ezetimibe's effect when added to ongoing non-statin lipid-lowering drugs or combination lipid-lowering therapy.", 'To evaluate the impact of preexisting lipid therapy on LDL-C response to ezetimibe.', 'We performed a retrospective review of all patients started on ezetimibe therapy at the Veterans Affairs Long Beach Healthcare System between March 1, 2003, and March 1, 2005. We calculated the ezetimibe-induced percent change in LDL-C in patients without concomitant changes in other lipid-lowering medications. We then stratified the population according to the type and number of preexisting lipid therapies and compared the LDL-C-lowering efficacy of ezetimibe among these groups.', 'Overall, ezetimibe was associated with a 23.0% reduction in LDL-C. Patients with preexisting statin monotherapy had significantly greater LDL-C reduction with ezetimibe than did those with preexisting non-statin drugs (-26.1% vs -9.3%; p = 0.0138). In patients with no preexisting lipid therapy (n = 58), monotherapy (n = 115), double therapy (n = 36), or triple therapy (n = 9), ezetimibe decreased LDL-C by 17.3%, 21.4%, 33.5%, and 38.1%, respectively. This stepwise trend in increased ezetimibe efficacy was statistically significant, even with adjustments for baseline LDL-C.'] Does type of preexisting lipid therapy predict LDL-C response to ezetimibe?