Adjuvant endocrine therapy is often advised for women with hormone receptor positive breast cancer. In premenopausal women, tamoxifen is the primary endocrine therapy option since aromatase inhibitors (AIs) are contraindicated in patients with residual ovarian function. The benefit of ovarian ablation/suppression in premenopausal patients remains controversial. In postmenopausal ER positive patients, treatment with an AI alone, switching strategies with an AI and tamoxifen, or extended therapy with an AI after 5 years of tamoxifen are superior to 5 years of tamoxifen alone. While the data supporting the use of endocrine therapy for ER positive breast cancer is clear, adverse effects occur with variable frequency and severity. The intensity and severity of the most common endocrine therapy adverse effects are mild to moderate for the majority of women, and serious life-threatening adverse effects are uncommon. However, compliance issues are often larger than recognized. Good communication with patients is critical to address concerns and symptoms, and more research is needed to identify effective methods to minimize treatment side effects.