Aromatase inhibitors (AIs) are becoming the hormonal treatment of choice for postmenopausal women with early breast cancer. Large, well-controlled clinical studies have established the efficacy and safety of initial adjuvant therapy with letrozole or anastrozole versus the previous standard of 5 years of adjuvant tamoxifen and support using an AI (exemestane, anastrozole or letrozole) following tamoxifen for 2-3 years (early 'switch' treatment) or 5 years (extended adjuvant treatment). Reducing recurrence risk is a primary goal of adjuvant hormonal therapy. There is an early peak of recurrences 2 years after surgery; most are distant metastases rather than local or regional events. Therefore, treatment strategies such as initial therapy with AIs, which reduce early distant recurrence events, can be expected to improve long-term survival outcomes. Switching to an AI following 2-3 years of initial adjuvant tamoxifen is an effective option for patients unable to begin treatment with an AI.