To measure the association between use of estrogenic botanical supplements and serum sex hormones in postmenopausal breast cancer survivors, a total 502 postmenopausal women were queried 2-3 years after breast cancer diagnosis about their use of botanical supplements, and supplements were categorized according to their estrogenic properties. Concurrently, a fasting blood sample was obtained for assay of estrone, estradiol, free estradiol, testosterone, free testosterone, dehydroepiandrosterone sulfate (DHEAS), and sex hormone-binding globulin. Adjusted means of the serum hormones were calculated by use of estrogenic supplements. Women reporting use of any estrogenic botanical supplement had significantly lower levels of estrone (20.8 vs. 23.6 pg/ml), estradiol (12.8 vs. 14.7 pg/ml), free estradiol (0.29 vs. 0.35 pg/ml), and DHEAS (47.7 vs. 56.2 microg/dl) compared to women reporting no use. Data from this cross-sectional study suggest the use of estrogenic botanical supplements may be associated with sex hormone concentrations in breast cancer survivors. Considering the high use of these supplements among breast cancer patients, further research is needed to clarify the relative estrogenicity/antiestrogenicity of these compounds and their relation with prognosis.