Adjuvant hormonal therapy results in substantial improvements in disease-free and overall survival for women with operable breast cancer. Use of an aromatase inhibitor (AI) is expected to replace tamoxifen as standard care for many patients. Aromatase is the enzyme responsible for the final step in estrogen biosynthesis. This is the conversion of the androgens testosterone and androstenedione to the estrogens estrone and estradiol. AIs are potent inhibitors of estrogen production and thus one of the major concerns over their use is their effect on bone health and their potential to increase the incidence of osteoporosis and risk of fracture. The American Society of Clinical Oncology has recognized that these patients are at high risk of developing osteoporosis and has published guidelines to aid in their management. These recommend that all patients have an initial dual-energy X-ray absorptiometry (DEXA) bone scan to assess bone mineral density and are offered calcium and vitamin D supplements as well as lifestyle advice. Patients with osteoporosis should be treated with a bisphosphonate to reduce the incidence of fracture. Osteonecrosis of the jaws is a recently described adverse side-effect of bisphosphonate therapy and has been described in women with metastatic breast cancer. Oversuppression of bone turnover is probably the primary mechanism for the development of this condition. The degree of risk for osteonecrosis with bisphosphonates is uncertain and warrants careful monitoring.