Fragility fractures are now recognized as a major public health problem. Although the prevalence of all fractures is similar among men and women, the vast majority of osteoporotic fractures occur in elderly women. These comprise vertebral compression fractures, Colles' fracture at the wrist and hip fracture, and to a lesser extent fractures at other sites. The fracture of greatest socioeconomic consequence in Europe is hip fracture, which increases exponentially in incidence with age. The reasons for differences in age- and sex-specific incidence relate in part to the lower bone density of women at the time of maturity (peak bone density) and the accelerated bone loss that occurs after the menopause. Women live significantly longer than men, so that the prevalence of osteoporosis amongst elderly women is six-fold that of men. The age-specific incidence of hip fracture is rising in men and women in many countries, and if the current trends in the United Kingdom continue then the number of hip fractures occurring each year will more than double over the next 20 years. There is a marked geographic distribution in the incidence of hip fractures, even in Europe. Indeed the differences in incidence between communities is greater than the differences in incidence between sexes within communities. This suggests that the importance of gonadal insufficiency in women has been overemphasized and that other factors, probably relating to genetic or lifestyle factors affecting peak bone density, account for ecological differences in incidence of hip fracture between communities.