Polycystic ovarian syndrome (PCOS) is the most frequent endocrine disorder of reproductive age women, affecting an estimated 8-10% of all women in this age group or approximately six million women. Further, women with PCOS continue to manifest the metabolic alterations inherent in the insulin resistance syndrome after menopause, rendering them more susceptible to type 2 diabetes and cardiovascular disease. Aging and obesity further contribute to these risks. Since estrogen-containing therapy is commonly used for menstrual regulation in premenopausal women with PCOS, it is important to evaluate the possible consequences of hormonal therapy on subsequent metabolic and cardiovascular risk. In postmenopausal women, a consensus regarding the appropriate role of estrogen replacement therapy is currently in evolution. By examining the effects of estrogen with or without progesterone on insulin resistance, insight may be gained about the risk/benefit ratio of this therapy in the subset of women with insulin resistance, PCOS, and type 2 diabetes. The goal of this review, then, is to examine the known effects of estrogen on insulin sensitivity and its implications for cardiovascular and metabolic risk.