Neoplasia affecting the skeleton is an important cause of morbidity, which includes hypercalcaemia, bone pain and fracture. In most instances these events are mediated by an increase in the resorption of bone which decreases bone density and disrupts skeletal architecture, either at focal sites or generally throughout the skeleton. Neoplastic activation of bone resorption in heterogeneous, but there is now good evidence that this is due to the increased activation of osteoclasts, the cells which mediate bone resorption in health. Bisphosphonates are specific inhibitors of osteoclast-mediated bone resorption and are capable of inhibiting osteoclastic activation independent of the mechanism of its stimulation. This provides the rationale for the use of bisphosphonates in the hypercalcaemia of malignancy. Despite refinements in the use of endocrine therapy, chemotherapy and radiotherapy these interventions have had relatively little impact on the skeletal morbidity or mortality of common malignancies affecting the skeleton, particularly breast cancer and myelomatosis. In addition, there is good evidence that skeletal disease is progressive in many patients despite the use of chemotherapy and radiotherapy. Since accelerated bone resorption can be inhibited by long-term treatment with bisphosphonates, their use is likely to decrease skeletal complications such as bone pain and fracture. The bisphosphonates, therefore, hold great promise as agents to improve the quality of life of such patients.