Objective There remains a large degree of disagreement about the association of polycystic ovary syndrome (PCOS) with impaired endothelial dysfunction and cardiovascular disease (CVD) risk. The purpose of this study was to determine whether overweight and obese women with PCOS have impaired endothelial function compared with weight-matched controls without PCOS and whether endothelial function is associated with cardiovascular risk markers and hormonal parameters. Design Cross-sectional analysis. Setting An outpatient trial at the Commonwealth Scientific Industrial Research Organisation Clinical Research Unit. Population Overweight and obese women with PCOS (n = 12) and weight-matched controls without PCOS (n = 10). Methods Endothelial function, cardiovascular risk markers and hormonal parameters were assessed in the patients. Main outcome measures Endothelial function was assessed by flow-mediated dilatation (FMD) of the brachial artery using high-resolution ultrasound. Lipid profile, fasting insulin level, glucose level, insulin resistance, C-reactive protein level, folate level, Vitamin B12 level and hormonal parameters. Results Women with PCOS had significantly higher testosterone levels (P