The authors have studied 8 patients with Homozygous Familial Hypercholesterolemia (FHO) an autosomal genetic dominant disease due to mutation of the gene encoding a cell surface receptor for LDL. Anatomic and pathologic abnormalities caused by LDL-cholesterol and B-Apolipoprotein high plasma levels were found. We also measured malondialdehyde levels in plasma and atherosclerotic plaques of the only autoptic case observed. MDA-levels are an index of lipid peroxidation. Cutaneous xanthomatosis lesions and severe cardiovascular disease were also present