 Background: Polycystic ovary syndrome PCOS is as common as 5-10 of all women in Austria. PCOS women frequently present with metabolic disturbances, hyperandrogenism and infertility. New therapy concepts are warranted. In our recent pilot study, vitamin D vitD supplementation significantly improved glucose metabolism and fertility. However, the efficacy of vitD administration shows individual variability indicating endogenous influences on pharmacological effects. 