The underlying pathophysiological determinants of the clinical features of polycystic ovary syndrome (PCOS) are a disturbance in ovarian and systemic biochemistry/endocrinology. Women with PCOS present a challenge when undergoing in vitro fertilization (IVF) because they may respond sensitively to stimulation. As insulin resistance and hyperinsulinaemia contribute significantly to the pathophysiological process in PCOS, it would be rational to assume therefore that pharmacological agents that modulate insulin sensitivity should improve the symptoms of PCOS. Whilst adjunctive treatment (metformin and clomiphene) was associated with higher ovulation and clinical pregnancy rates (CPR) this did not translate to higher live birth rates, and as such its use in ovulation induction is limited. Metformin treatment was associated with a reduction in the incidence of ovarian hyperstimulation syndrome (OHSS). It may improve follicular growth and development and as such improve the developmental potential of the embryo.