The skeleton is the most common organ to be affected by metastatic cancer and the site of disease that produces the greatest morbidity. Skeletal morbidity includes pain that requires radiotherapy, hypercalcemia, pathologic fracture, and spinal cord or nerve root compression. From randomized trials in advanced cancer, it can be seen that one of these major skeletal events occurs on average every 3 to 6 months. Additionally, metastatic disease may remain confined to the skeleton with the decline in quality of life and eventual death almost entirely due to skeletal complications and their treatment. The prognosis of metastatic bone disease is dependent on the primary site, with breast and prostate cancers associated with a survival measured in years compared with lung cancer, where the average survival is only a matter of months. Additionally, the presence of extraosseous disease and the extent and tempo of the bone disease are powerful predictors of outcome. The latter is best estimated by measurement of bone-specific markers, and recent studies have shown a strong correlation between the rate of bone resorption and clinical outcome, both in terms of skeletal morbidity and progression of the underlying disease or death. Our improved understanding of prognostic and predictive factors may enable delivery of a more personalized treatment for the individual patient and a more cost-effective use of health care resources.