Women with polycystic ovary syndrome (PCOS) frequently present with reproductive dysfunction. Ovarian function might be disturbed, with resultant abnormal folliculogenesis and steroidogenesis and, although it is difficult to define the exact pathogenesis of anovulation, many possible mechanisms have been postulated. Folliculogenesis in anovulatory women with PCOS is characterized by failure of dominance and the ovary has multiple small follicles, which are arrested but capable of steroidogenesis. Abnormalities in gonadotrophin and insulin secretion and disordered paracrine function have been identified. Women with PCOS have an increased prevalence of miscarriage, both after spontaneous and induced ovulation. Hypersecretion of LH, hyperandrogenaemia and hyperinsulinaemia have all been investigated as possible causes of PCOS. It is likely that these factors are interlinked and together might result in disordered ovarian and endometrial function. Multiple other possible abnormalities have been postulated as contributory factors in the reproductive failure. These include decreased plasminogen activator inhibitor activity, endothelial dysfunction and obesity. Ideally, therapy should target the underlying disorders but at present data are inadequate and further investigations are essential before therapeutic recommendations are truly based on an understanding of the pathophysiology.