PCOS is a common, complex endocrinopathy, which can cause women of childbearing age trying to become pregnant considerable problems. In addition, it is associated with an appreciably elevated risk for miscarriage. For modern techniques of assisted reproduction, PCOS poses a particular problem, since, on account of a lack of response, patients either abandon treatment significantly more frequently, or else suffer threatening complications manifesting as a severe hyperstimulation syndrome. In view of new knowledge of the pathomechanism of PCOS, highly effective interventional options with insulin sensitizers, and in particular the oral antidiabetic, metformin, are now available in addition to the classical stimulation regimes for the treatment of infertility.