Objective: To determine whether or not plasma advanced oxidation protein products (AOPPs) are associated with known cardiovascular risk factors or carotid intima-media thickness (IMT) in patients with polycystic ovary syndrome (PCOS). Design: A prospective, controlled study. Setting: University hospital. Patient(s): Forty-six women with PCOS and 46 age- and body mass index-matched healthy women. Intervention(s): Carotid IMT was evaluated for both common carotid arteries. We measured serum levels of AOPP, homocysteine (Hcy), C-reactive protein (CRP), malonyldialdehyde (MDA), vitamin B 12, folate, lipid, and hormone profiles. The presence of insulin resistance was investigated by means of homeostasis model assessment (HOMA). Main Outcome Measure(s): Serum AOPP, fasting insulin, HOMA index, Hcy, MDA, CRP, and carotid IMT, Result(s): The women with PCOS had significantly higher serum AOPP than control women. High AOPP was defined as equaling or exceeeding the mean + 2 SD of the plasma AOPP in control subjects (56.2 pg/mLI). Carotid IMT, fasting insulin, HOMA index, Hcy, MDA, and CRP were signficantly higher in PCOS patients with high AOPP than in those with normal AOPP. Fasting insulin, insulin resistance, and Hcy were independent determinants of plasma AOPP. Conclusion(s): Increased AOPP may contribute to the increased risk of atherosclerotic cardiovascular disease in women with PCOS. (Fertil Steril (R) 2009;92:1372-7. (C)2009 by American Society for Reproductive Medicine.)