Oslo, Norway has the highest incidence of hip fractures ever reported. There are great differences in life expectancy between city regions in Oslo, and we investigated if there were any differences in incidence of hip fracture within the city. In 1989, all new fractures of the proximal femur in Oslo residents 50 years or older were registered with each patient's address. Patients in nursing homes were registered according to preadmission address. All were localized to one of six city regions. The incidence of fracture of the total population of Oslo in 1 year age groups was projected on the population of the city regions to calculate the expected number of fractures compared with all of Oslo. The ratio between observed and expected number of fractures was calculated for each city region. The rural county of Sogn og Fjordane (S&F) has only two thirds the incidence of hip fractures compared with Oslo, and life expectancy is longer for both genders compared to Oslo. New hip fractures in 1989 were registered in S&F as in Oslo, and the ratio between observed and expected number of fractures calculated as for Oslo city regions. There were 1029 new fractures in Oslo women, and 284 in men. The relative risk (RR) for Oslo city regions using Inner Oslo West as the reference, showed significantly higher RRs for hip fracture in Inner Oslo East in women (1.23, 95% confidence interval 1.03-1.48) and in Inner and Outer Oslo East in men (1.67, 95% confidence interval 1.14-2.24; 1.45, 95% confidence interval 1.00-2.11, respectively). The risk in S&F compared with Inner Oslo West was significantly lower for women, but not for men (RR 0.74, 95% confidence interval 0.60-0.92; RR 0.82, 95% confidence interval 0.56-1.21, respectively). There were differences in annual incidence of hip fractures between different city regions in Oslo for both women and men, and the incidences were higher than in the rural county of S&F.