Bone metastases are a common problem in the management of breast cancer and are associated with considerable morbidity. Bone pain, hypercalcaemia, fractures and cord compression all occur requiring interventions such as analgesia, radiotherapy and surgery. Bisphosphonates are drugs that are active in the bone microenvironment. Their effects on osteoclasts are well described: they potently inhibit osteoclast mediated bone resorption by delaying the maturation of immature osteoclasts and by directly inducing osteoclast apoptosis. It has been known for some time that bisphosphonates, in combination with intravenous rehydration, effectively treat hypercalcaemia associated with solid malignancies. It has now been demonstrated in clinical trials in breast cancer patients that regular bisphosphonate administration reduces the morbidity associated with osteolytic skeletal metastases. There is an emerging suggestion from clinical trial work that bisphosphonates may be able to reduce or delay the development of skeletal metastases although this remains controversial as the three published trials present conflicting results. The more potent third-generation bisphosphonates, such as zoledronate, are now being tested for each of these indications with promising results and may replace other bisphosphonates in the future. Laboratory studies have recently demonstrated that bisphosphonates have direct cytotoxic effects against breast cancer cells in vitro, inducing apoptosis and preventing adhesion to bone. This adds support to the hypothesis that bisphosphonates may have a genuine beneficial effect in the adjuvant setting.