For more than 100 years ovarian ablation has been used as treatment for breast cancer. There are several methods of ovarian ablation including surgical oophorectomy, radiation-induced ablation, and chronic use of luteinizing hormone-releasing hormone (LHRH) analogs. In addition, there is some suggestion that cytotoxic chemotherapy may act in part by inducing ovarian ablation in premenopausal breast cancer patients. Of the numerous case series and clinical trials of ovarian ablation performed in the past century, many have been fraught with methodologic problems. The Early Breast Cancer Trialists' Collaborative Group (EBCTCG) meta-analysis of 12 properly randomized trials shows a significant improvement in disease-free survival (DFS) and overall survival for women who underwent ovarian ablation as adjuvant therapy compared with those who did not. However, a number of questions remain. The relative efficacy of chemotherapy and ovarian ablation and the value of combining ovarian ablation with chemotherapy or other endocrine therapy have not yet been determined. This articles reviews and compares the methods of ovarian ablation, and discusses the EBCTCG overview data, as well as the newer and ongoing trials, which may answer the remaining questions about the optimal use of this therapy in the adjuvant treatment of breast cancer.