The skeleton is the most common organ to be affected by metastatic cancer, and tumors arising from the breast, prostate, thyroid, lung, and kidney possess a special propensity to spread to bone. Breast carcinoma, the most prevalent malignancy, causes the greatest morbidity. Of great clinical importance is the observation that metastatic bone disease may remain confined to the skeleton. In these patients, the decline in quality of life and eventual death is due almost entirely to skeletal complications and their subsequent treatment. Bone pain is the most common complication of metastatic bone disease, resulting from structural damage, periosteal irritation, and nerve entrapment. Recent evidence suggests that pain caused by bone metastasis may also be related to the rate of bone resorption. Hypercalcemia occurs in 5-10% of all patients with advanced cancer but is most common in patients with breast carcinoma, multiple myeloma, and squamous carcinomas of the lung and other primary sites. Pathologic fractures are a relatively late complication of bone involvement. The clinical courses of breast and prostate carcinoma are relatively long, with a median survival of 2-3 years. For patients with breast carcinoma, good prognostic factors for survival after the development of bone metastases are good histologic grade, positive estrogen receptor status, bone disease at initial presentation, a long disease free interval, and increasing age. In addition, patients with disease that remains confined to the skeleton have a better prognosis than those with subsequent visceral involvement. For patients with prostate carcinoma, adverse prognostic features include poor performance status, involvement of the appendicular skeleton and visceral involvement, whereas for patients with multiple myeloma, the levels of serum beta2-microglobulin and lactate dehydrogenase and the immunologic phenotype are the most important factors. These prognostic factors may be useful in planning the rational use of bisphosphonates in the treatment of advanced cancer.