The primary objective of this study is to evaluate the efficacy and the safety of ezetimibe (SCH 58235) co-administered with either atorvastatin or simvastatin in participants with homozygous familial hypercholesterolemia (FH).

Inclusion Criteria:

• With a diagnosis of homozygous familial hypercholesterolemia
• All females must have a negative pregnancy test prior to study entry. Women of child bearing potential must agree to practice an effective barrier method of birth control for the duration of the study, until one month after treatment.
• Postmenopausal women who are receiving postmenopausal hormonal therapy or raloxifene must be maintained on a stable estrogen (ERT), estrogen/progestin (HRT) or raloxifene regimen during the study period. ERT, HRT or raloxifene cannot be changed during study period.
• Must follow prescribed or stricter diet, and demonstrate completion of Diet Diaries

Exclusion Criteria:

• A history of mental instability, drug or alcohol abuse; or have been treated or are being treated for severe psychiatric illness which, in the opinion of the Investigator, may interfere with optimal participation in the study.
• With underlying disease likely to limit life span to less than 1 year.
• Have previously been randomized in any studies examining ezetimibe
• Pregnant or lactating women.
• With known hypersensitivity or any contraindication to statin therapy.