Infertility is a common manifestation of the polycystic ovary syndrome (PCOS), a condition characterized by chronic anovulation, hyperinsulinemia and hyperandrogenism. Hyperinsulinemia leads to increased ovarian androgen production, resulting in follicular atresia and anovulation. Metformin, a medication that improves insulin sensitivity and decreases serum insulin levels, restores menstrual cyclicity and ovulatory function and may improve fertility rates in women with PCOS. We present three consecutive cases from our clinic that support this premise. Three patients were seen in the reproductive endocrinology clinic with documented PCOS, long-standing infertility and clinically diagnosed insulin resistance. The first patient had hyperandrogenic, insulin-resistant acanthosis nigricans syndrome and had been resistant to multiple courses of clomiphene citrate; the second exhibited hypertension, hyperlipidemia and glucose intolerance along with anovulation; and the third presented with poorly controlled type 2 diabetes and a desire to conceive. Each patient received metformin, which led to restoration of menstrual cyclicity and conception in all three cases. These three patients reflect the heterogeneous nature of PCOS, and treating their underlying insulin resistance with metformin resulted in pregnancy. These findings suggest that metformin may be a useful adjunct for treatment of infertility in patients with PCOS.