Increasing age remains the major risk factor for breast cancer and more than half of all breast cancers in North America and the European Union occur in women 65 years and older. Anticipated life expectancy, co-morbidity, and functional status must all be considered when offering systemic adjuvant treatment to older women. Tamoxifen significantly decreases the risk of recurrence and improves survival in all women with hormone receptor-positive invasive breast cancer, including women 70 years and older. More recently, aromatase inhibitors have been shown to be even more effective than tamoxifen in reducing breast cancer recurrence in postmenopausal women, and are an appropriate choice for initial endocrine therapy in older women. Adjuvant chemotherapy improves survival in postmenopausal women, but adds little to endocrine therapy in the majority of women with node-negative, hormone receptor-positive tumors. Chemotherapy should be considered for patients with high-risk node-negative, hormone receptor-negative tumors and those with node-positive tumors. Co-morbidity and its effect on survival should be factored into all chemotherapy decisions. Older women are frequently under-treated and are still under-represented in clinical trials; sometimes this represents good clinical judgment, but age bias alone can result in under-treatment and higher breast cancer-related mortality or state-of-the-art trials not being offered to older, but otherwise eligible, patients. Physician education and more clinical trials designed for older women are needed.