Breast cancer is a hormone-sensitive cancer and in most post-menopausal women hormone receptor positive. The hormone receptor status is a highly valid predictive marker of responsiveness to endocrine therapy. The standard adjuvant therapy in patients with hormone-receptor-positive breast cancer is the selective estrogen receptor modulator tamoxifen. Third-generation aromatase inhibitors are accepted as a treatment option for metastatic breast cancer. However, results from recent studies show also a benefit of this type of drugs for disease-free survival with fewer adverse reactions in the adjuvant therapy. Therefore a new therapeutic field opens for the use of 3rd-generation aromatase inhibitors. This will lead to an expansion of the indication, but the question of modality -- up-front, switch or extended therapy -- remains to be resolved.