From 1970 to 1986 a total of 4578 hip fractures were registered in persons > or = 40 years in a Danish urban municipality. During that period, the annual number almost tripled. The statistical analysis revealed an increase in the age-specific incidence for both females and males (p < 0.0001). Furthermore, the number of fractures increased due to demographic aging. The overall incidence for individuals > or = 40 years increased 9-10% annually; from 2.1 to 5.4 per 1.000 females, and from 0.9 to 2.1 per 1.000 males. The female:male ratio was 2.8 without changes over time. If the observed increase in incidence is extrapolated to the next 17 years, a doubling of the annual number of fractures is predicted by the year 2002, whereas an unchanged incidence would result in a 20% increase in number.