Summary. Tamoxifen is considered to be the gold standard in hormonotherapy of patients with estrogen dependent breast cancer (estrogen receptor (ER) and/or progesterone receptor (PR) positive tumors). However, because tamoxifen’s benefi- cial effects diminish after 5 years of use in adjuvant setting and because of its partial agonistic effects and its resistence to tamoxifen in some breast carcinoma, there is a need for new antiestrogens. One of these antiestrogens is fulvestrant which, unlike tamoxifen, has no partial agonistic effects. Its efficacy has been confirmed in preclinical and in recent phase III clini- cal studies in postmenopausal patients. In disease recurrence after adjuvant tamoxifen or progressive disease on-first-line tamoxifen treatment fulvestrant is comparable with (similar to) anastrozole. When compared with tamoxifen as first-line treatment in patients with advanced cancer, only in patients with ER and/or PR positive tumors similar results have also been obtained. In both trials tolerance to fulvestrant has been good. Following the results of these clinical studies fulvestrant has already been licenced in the USA and EU for the treatment of postmenopausal women with advanced breast cancer who had progressed on prior anti-estrogen therapy.