Fragility fractures are now recognised as a major problem of public health. 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 fractures at the wrist, and hip fracture, and to a lesser extent fractures at other sites. The incidence of vertebral and hip fracture increases exponentially with age. The reasons for this 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- and sex-specific incidence of osteoporotic fracture is rising in many countries, and if the current trends in the United Kingdom continue, then the number of hip fractures each year will more than double over the next 20 years. There is a marked geographic distribution in the incidence of hip fracture, and probably of other osteoporotic fractures. Indeed, the difference in incidence between communities is greater than the difference in incidence between sexes within communities. This suggests that the importance of gonadal insufficiency in women has been over-emphasised and that other factors, probably relating to life-style factors affecting peak bone density, account for ecological differences in incidence between communities and secular trends within communities.