Osteoporosis is an increasing health care concern as populations age throughout the developed and developing world. The social and economic costs of osteoporosis are due to its clinical outcome of fracture which increases exponentially with age. This review will highlight some of the key epidemiological aspects of osteoporosis incorporating areas of more recent interest. These include the definition; the magnitude of the problem encompassing differing incidence and prevalence patterns of both low bone mass and fracture in different cultural groups; the social consequences of fracture, including economic costs, morbidity and mortality; the evaluation of fracture risk, including the role of bone density, bone quality and the risk of falling; as well as an overview of some of the factors involved in determining low bone mass. Bone mineral density (BMD) is the most easily measured and accurate predictor of fracture risk. For any individual, BMD is the combination of their peak bone density and subsequent bone loss, both of which are influenced by genetic, hormonal and environmental factors. An understanding of key issues relating to this important disease may lead to earlier detection of the individual at high risk for fracture and rational approach to prevention and management.