There is a little information in literature about circulating asymmetric dimethylarginine (ADMA) concentrations in polycystic ovary syndrome (PCOS) and the results reported are discrepant. In this study, therefore, we aimed (1) to determine the circulating ADMA concentrations in 44 women with PCOS and 22 age- and BMI-matched healthy controls, (2) to evaluate its correlations with insulin resistance, gonadotrophins, and androgen secretion, and (3) to compare effects of metformin and ethinyl estradiol-cyproterone acetate (EE/CPA) treatments on circulating ADMA concentrations. In conclusion, our data indicate that circulating ADMA concentrations in non-obese, non-hypertensive and young women with PCOS are significantly higher than healthy controls and they improved by a 3-month course of metformin and oral contraceptive treatments.