Endocrine therapy is now established as the treatment option of choice for postmenopausal women with hormone receptor-positive advanced breast cancer. The benefit of the third-generation aromatase inhibitors (AIs) in this setting has prompted their evaluation in the treatment of early breast cancer. This article reviews the current clinical status of AIs as adjuvant therapy for early-stage breast cancer in postmenopausal women, focusing on the largest adjuvant breast cancer study till date to provide data, the ‘Arimidex’, Tamoxifen, Alone or in Combination (ATAC) trial.