Tamoxifen has been the ‘gold standard’ treatment for advanced breast cancer in postmenopausal women for several years. However, data presented at the 10th European Conference on Clinical Oncology [Vienna, Austria; September 1999] challenges this dominant position. Anastrozole [‘Arimidex’] has been shown to be at least as effective and well tolerated as tamoxifen in a multinational trial, and data from a North American trial indicate that anastrozole is more effective.