Breast cancer is the most common malignancy in women, and the incidence of breast cancer increases with increasing age until age 80. As the population continues to age, breast cancer in older women will become an increasing clinical challenge. A majority of breast cancer in older women is hormone receptor-positive, making hormonal therapy the mainstay of adjuvant treatment in this group. Chemotherapy clinical trials have largely excluded the elderly, and therefore limited data exists on the efficacy and tolerability of standard adjuvant chemotherapy in older women. Ongoing studies are addressing alternatives to standard adjuvant chemotherapy in this group. Emerging biologic instruments such as gene-expression profiling may be able to better identify patients who will gain benefit from adjuvant chemotherapy. Elderly patients are highly variable in their functional status, reserve capacity, and comorbidity, and better assessment tools are needed to evaluate these issues and predict which patients will tolerate cancer treatments. More work is needed to address the many challenges that affect the adjuvant treatment of breast cancer in older women.