Fulvestrant (Faslodex, formerly ICI 182,780) is a potent steroidal antiestrogen that mediates its effects by estrogen receptor downregulation. It appears to act as a pure antiestrogen and exhibits none of the negative side effects associated with the partial agonist activity of tamoxifen. It has been shown to be as effective as the oral aromatase inhibitor anastrozole in postmenopausal women with advanced breast cancer who have progressed on prior endocrine therapy, principally tamoxifen. It therefore provides the clinician with an alternative therapeutic strategy following the development of tamoxifen resistance. Fulvestrant might also have potential as a follow-on therapy after tamoxifen in an adjuvant setting and help alleviate some of the concerns surrounding long-term (up to 5 years) tamoxifen therapy.