Oxidative modification of LDL has been proposed as an early and crucial step in the development of atherosclerosis, and antibodies against such modified LDL are found in both healthy individuals and patients with atherosclerosis. In this study, 62 patients who were surgically treated for peripheral arterial occlusive disease below the age of 50 were investigated and compared with age- and sex-matched healthy individuals in a case-control study. Autoantibodies against oxidized LDL were measured with an enzyme-linked immunosorbent assay method. Risk factors such as smoking, hypertension, family history of premature cardiovascular events, and lipoprotein levels were also determined. The patients had significantly higher levels of autoantibodies against oxidized LDL; significantly higher levels of total cholesterol, LDL cholesterol, triglycerides, and apo A-I; and significantly lower levels of HDL cholesterol than did control subjects. In multivariate analyses autoantibodies against oxidized LDL discriminated better between patients and control subjects than did any of the different lipoprotein analyses. Among patients, the presence of hypertension and a family history of cardiovascular events were the only factors significantly associated with increased levels of autoantibodies against oxidized LDL.