The polycystic ovary syndrome is a common cause of anovulatory infertility. Women with severe insulin resistance are a unique subset of polycystic ovary syndrome. The syndrome of hyperandrogenism, insulin resistance, and acanthosis nigricans (HAIR-AN syndrome) is one presentation of the insulin-resistant subset of polycystic ovary syndrome. Insulin resistance and hyperandrogenism are caused by genetic and environmental factors. In women with anovulatory infertility caused by hyperandrogenism and insulin resistance, clomiphene citrate treatment often fails to result in pregnancy. For these women, weight loss and insulin sensitizers can be effective methods of inducing ovulation and pregnancy and may reduce the number of clomiphene-resistant women with polycystic ovary syndrome who are treated with gonadotropins, ovarian surgery, or in vitro fertilization-embryo transfer.