Osteoporosis is the most common metabolic bone disease. It is characterised by reduced bone mass, altered bone architecture and the clinical consequence of easy fracture with little or no trauma (low-trauma fractures). These fractures tend to occur most commonly in sites of the skeleton that are rich in trabecular bone: the wrist, spine and hip. It is the last of these which has the greatest morbidity and mortality, but all osteoporotic fractures result in pain and suffering for patients and have considerable socio-economic impact on healthcare systems and society generally (Cooper 1996). Over the past decade there has been considerable improvement in the therapeutic interventions that can be made to increase bone mineral density (BMD) and, more importantly, reduce future fracture risk (Royal College of Physicians 1999, 2000). Such therapies include bisphosphonates (etidronate, alendronate, risedronate) and selective oestrogen modulator regulators (SERMs). These therapies have been added to hormone replacement therapy (HRT), which is known to be effective in preventing the bone loss that occurs in post-menopausal women. These developments have made it even more relevant to identify accurately those patients at risk of osteoporosis, and to do so before they suffer a fracture.