We studied the most complete skeletons found in an excavation from the 14th and 15th century in central Stockholm. One hundred eighty-seven were from men and 156 from women: 241 individuals were estimated to be between 20 and 39 and 102 between 40 and 59 years old at death. We examined the bones radiographically and by dual photon absorptiometry. The bone mineral density (BMD) was similar to the finding in North America and Northern Europe today as was the relationship between men and women. However, there appeared to be a higher diaphyseal bone density in the lower extremities, especially in men. The femur score was higher and the BMD of the femoral and tibial shafts was higher than today. In the upper extremities the diaphyseal bone density was lower. Meema's index, as well as the metacarpal score, was smaller than in individuals in this century and the BMD of the humeral shaft was also lower than seen today. Overall, the metaphyseal bone density was similar to what we now consider normal; i.e., the mean BMD of the femoral neck was 0.96 g/cm2 in men and 0.90 g/cm2 in women and of the distal radius 0.43 and 0.32 g/cm2, respectively. The low diaphyseal density and in the upper extremities may be related to the nutritional status, whereas the greater need for walking and standing in the 14th and 15th century might have led to the high diaphyseal density in the lower extremities. There was no evidence of bone loss after 40 years of age in either sex in our study. The average expected lifespan for an adult individual was less than 50 years and we suggest that the relatively high bone density in the older age group may be due to selection of the most physically fit. The activity pattern, therefore, may be considered the most important determinant for the differences.