The aim of the study was to determine whether menopause is followed by endosteal resorption and periosteal apposition, and if so, whether geometric changes in bone were associated with the post-menopausal serum estradiol levels. The second aim was was to see if periosteal apposition compensated for the decrease in tissue mineral content and whether a strength index that accounts for both tissue density and geometric properties might be a better predictor than bone meneral density alone of future fracture of the distal radius. Bone mass and the skeletal structure of the distal radius were evaluated by single-photon absorptiometry every other year in 108 women, who were followed from the time of menopause for a mean period of 15 years. The mean annual decrease in bone mineral density was 1.9±0.7 percent. The medullary bone diameter increase annually by 1.1±0.9 percent and periosteal diameter by 0.7±0.3 percent; the strength index decreased by 0.7±0.7 percent. The postmenopausal serum estradiol level was correlated with changes in the periosteal diameter and with changes in bone mineral density. A 1-SD decrement in the strenth index at base line was associated with a risk ratio for fracture of the distal radius of 3.8. Increased bone loss after menopause is associated with increased periosteal apposition, which partially preserves bone strength. A strength index may be a helpful predictor of the risk of fracture.