The third-generation aromatase inhibitors (AIs) have improved efficacy and safety versus tamoxifen for treatment of advanced breast cancer. Currently, anastrozole is the only third-generation AI with adjuvant therapy data in postmenopausal women. Initial and updated results from the Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial (median follow-up, 47 months) confirm it to be more effective than tamoxifen for disease-free survival with several important tolerability benefits. As a result, there has been much debate about whether or not anastrozole should be used routinely to treat postmenopausal women with early breast cancer. In its review, the American Society of Clinical Oncology Health Services Research Committee agreed that the updated ATAC analyses provided a greater level of assurance, in terms of both toxicity and efficacy, for use of anastrozole in the adjuvant setting. However, pending 5-year data from ATAC and other trials of adjuvant AI use, adjuvant anastrozole was recommended by American Society of Clinical Oncology Health Research Committee for use only under certain circumstances, with 5 years of tamoxifen remaining the standard. Anastrozole should be the preferred AI in this setting; data from the ATAC trial should not be extrapolated to other members of the class. Despite this conservative recommendation, the overall risk:benefit profile from the ATAC trial favors anastrozole, and it is expected that a more favorable efficacy and adverse effect profile will be maintained. Anastrozole should, therefore, now be considered a valid alternative option to tamoxifen for adjuvant hormonal treatment in all postmenopausal women with hormone receptor-positive early breast cancer.