The new non-steroidal and steroidal aromatase inhibitors are at least as effective as megestrol acetate (MA) as second-line hormonal agents in postmenopausal women with breast cancer. However, they are superior to MA in terms of tolerability and adverse effects. Letrozole and exemestane have been shown to be superior to MA in terms of efficacy. Furthermore, exemestane and anastrozole demonstrated a survival advantage over MA. These drugs are therefore considered established second-line hormonal agents. There is a growing body of evidence supporting the role of third-generation aromatase inhibitors as first-line therapy for ER-and/or PgR-positive advanced breast cancer in postmenopausal women, and as a neoadjuvant therapy in postmenopausal women with hormone receptor positive tumours unsuitable for breast conserving surgery. Studies comparing these drugs head-to-head and with adjuvant tamoxifen are currently in progress. The potential role of these drugs in breast cancer prevention is worth investigating.