Fracture prevention requires the identification of individuals at risk prior to fracture. Bone density, a history of previous fractures, biochemical markers, and the frequency and types of falls are important risk factors for fractures. There are also many other risk factors for bone loss, falls, and fractures. When considered alone or in combination, risk factors can identify a wide range of fracture risk among individuals. Persons with multiple risk factors are at greater risk than are those with either a single risk factor or none. It is not possible to modify some risk factors such as age and gender. Although it is possible in theory to modify other risk factors such as calcium or vitamin D deficiency, the resulting benefits are often small. In contrast, the determination of BMD provides a precise, noninvasive measure of fracture risk, and effective treatments are available to prevent bone loss and increase BMD. Current BMD represents the cumulative, combined influence of all past and current risk factors for bone loss, and prospective changes in biochemical markers and BMD can be used to monitor treatment efficacy. Persons with low BMD and those with multiple risk factors may benefit the most from treatments to preserve or increase BMD. Bone density should always be measured directly, because it is not possible to predict this parameter and fracture risk from other risk factors for bone loss.