© 2021Objectives: Women with polycystic ovary syndrome (PCOS) have an increased cardiometabolic risk. Similarly, it was previously shown that atherosclerotic and cardiovascular risk is increased in the general population with lower serum Klotho levels. The aim of this study was to investigate the lotho and thiol/disulfide levels in women with non-obese PCOS compared to healthy controls and also to investigate the relationship of serum Klotho and thiol/disulfide homeostasis with cardiometabolic risk factors. Materials and methods: In this prospective case control study, human serum alpha Klotho levels and thiol/disulfide homeostasis of women with PCOS aged between 19-33 were compared to their age and BMI matched non – PCOS healthy controls. In addition, the correlation of these molecules with other metabolic markers/measurements were also investigated. Results: Metabolic parameters such as mean waist circumference, lipid accumulation product, visceral adiposity index, fasting insulin, homeostasis model assessment of insulin resistance and triglyceride values were higher in the PCOS group (p = 0.038, p = 0.008, p = 0.001, p = 0.001, p = 0.002 and p = 0.002, respectively) compared to controls. However, mean serum Klotho and native thiol levels (respectively p < 0.0001 and p = 0.038) were lower compared to controls. Correlation analysis revealed that serum Klotho levels were negatively correlated with BMI, waist circumference, disulphide/total thiol, disulphide/native thiol, HOMA-IR and LAP-index. Conclusions: Findings of decreased serum Klotho and native thiol values of the PCOS group compared to controls and the negative correlation of serum Klotho levels with metabolic markers supports the idea that decreased Klotho may be another mechanism by which cardiovascular risk is increased in women with PCOS.