Polycystic ovary syndrome (PCOS) represents a heterogeneous spectrum of disorders, mainly characterized by chronic oligoanovulation and hyperandrogenism. Although not included in the diagnostic criteria, insulin resistance is recognized as a fundamental pathogenetic factor of the syndrome. Thus, the use of insulin-sensitizing drugs, such as metformin and thiazolidinediones, has been proposed for PCOS treatment. These agents are unique because they exert both metabolic and endocrine/ovarian beneficial effects. In this review the results of up-to-date clinical studies and meta-analyses on the possible gynaecological actions of insulin sensitizers are discussed. It has been shown that, as well as favourable metabolic influences, such as improvement in glucose, lipid and proinflammatory profiles, these agents also exert beneficial endocrine and ovarian effects, including amelioration of reproductive abnormalities, restoration of ovulation and menstrual cycles, increase in pregnancy rates and reduction of androgen production. Therefore, current data support the use of insulin sensitizers, along with lifestyle measures and/or other agents, in women with PCOS, especially in the presence of insulin- or clomifene-resistance.