Objective To investigate oxidative stress and angiogenetic factors in polycystic ovary syndrome (PCOS). Design Prospective cohort study. Setting University outpatient clinic. Subjects Fifty women with PCOS were divided into two groups: body mass index (BMI) >27 kg/m2 (n = 25) and BMI <27 kg/m2 (n = 25). The control group consisted of 20 age- and BMI-matched healthy women. Intervention(s) None. Main Outcome Measure(s) Enzyme-linked immunosorbent assays were used to measure serum levels of 8-hydroxydeoxyguanosine (8-OHdG), angiopoietin-2, and vascular endothelial growth factor (VEGF). Result(s) Women with PCOS had significantly lower serum 8-OHdG levels (mean 137.8 pg/mL, range 53.4–282.9 pg/mL) compared with the control subjects (mean 219.78 pg/mL, 124.6–372.4 pg/mL). This difference was obvious in both lean (BMI <27 kg/m2 ) and obese (BMI >27 kg/m2 ) subjects. Concentrations of VEGF were higher among obese subjects with PCOS. Conclusion(s) Serum 8-OHdG levels are significantly lower in women with PCOS than in healthy controls. The clinical significance of this finding is discussed.