Treatment with adjuvant endocrine therapy, including tamoxifen and the aromatase inhibitors, has resulted in notable improvements in disease-free and overall survival for patients with hormone receptor-positive breast cancer. Despite their proven benefit, however, adherence to and persistence with the medications is poor in part because of bothersome side effects that can negatively affect quality of life. Retrospective analyses have identified possible predictors of development of toxicity. Reports have also suggested that development of toxicity may be a biomarker of better response to therapy. In addition, there has been considerable research investment into the management of these side effects, which may lead to improved adherence and persistence with therapy. However, although notable advances have been made, much more remains to be done to provide patients with truly personalized therapy for hormone receptor-positive breast cancer.