Osteoporosis is the most important cause of fracture in the elderly in the Western world. Estimates of fracture frequency in the UK vary, but the combined annual incidence of fracture of the vertebrae, hip, and distal forearm is approximately 200 000, of which the majority are associated with osteoporosis. An estimated 40% of women and 13% of men aged 50 years and older will sustain an osteoporotic fracture in their lifetime. Osteoporosis is an important cause of mortality and morbidity not only in the Western countries, because the number of elderly women is increasing worldwide, most rapidly in Asia, Latin America, the Middle East, and Africa. Although bone mineral density is closely associated with the risk of fracture, it does not account for all of the variation in fracture rate in the population. Age appears to be an important factor that is independent of bone mineral density.