Women with inherited or acquired thrombophilia are at increased risk for venous thromboembolism (VTE) when they use oral contraceptives (OCs) of either the second or third generation. For women who are heterozygous for Factor V Leiden, the risk is probably 28 to 50 of 10,000 women-years compared to 2 to 5 of 10,000 years for those not known to have thrombophilia. The thrombotic risk is highest during the first year that OCs are used. Whether women with thrombophilia are at increased risk for VTE when they use hormone replacement therapy (HRT) has not been assessed in any study. For women without thrombophilia, the risk for VTE associated with HRT is probably 2 to 3 of 10,000 years. The benefits of HRT include reduced risk for myocardial infarction and Alzheimer's disease, and increased bone density. The physiological changes induced by HRT are not the same as those induced by OCs. Small studies have suggested that for women who have additional risks of thrombosis (i.e., perioperative setting, underlying systemic lupus erythematosus), HRT does not confer the same increased risk of thrombosis, as does the use of OCs. Until data are available to address the magnitude of any increase in thrombotic risk induced by HRT for women with thrombophilia, physicians probably serve their patients best by providing information about the benefits of HRT, emphasizing that the risk of VTE is unknown, and encouraging patients to take an active role in decisions about their healthcare.