Several previous studies have reported regional differences in the incidence of hip fractures. A population-based study was performed in the city of Malmö (urban population) and in the municipality of Sjöbo (rural population), 60 km apart. A total of 961 men and women, randomly selected and of Scandinavian ethnic background, participated in the study. Bone mineral content (BMC) of the forearm was measured with single-photon absorptiometry (SPA). Women and men in the city had significantly lower BMC compared with the rural population. The differences were even more pronounced when comparing a true urban population (lived their entire life in a city) with a true rural population (never lived in a city). The differences in BMC between Malmö and Sjöbo were more obvious in men. These data suggest that differences in bone mass between an urban and a rural population could to some extent explain differences in fracture incidence.