In this cross-sectional study, we aimed to predict age-related changes in bone microarchitecture and strength at the distal radius (DR) and distal tibia (DT) in 644 Canadian adults (n = 442 women and 202 men) aged 20 to 99 years. We performed a standard morphologic analysis of the DR and DT with high-resolution peripheral quantitative computed tomography (pQCT) and used finite-element analysis (FEA) to estimate bone strength (failure load) and the load distribution. We also calculated a DR load-to-strength ratio as an estimate of forearm fracture risk. Total bone area, which was 33% larger in young men at both sites, changed similarly with age in women and men at the DT but increased 17% more in men than in women at the DR (p < .001). Trabecular number and thickness (Tb.Th) were 7% to 20% higher in young men than in young women at both sites, and with the exception of Tb.Th at the DR, which declined more with age in men (−16%) than in women (−2%, p < .01), the age-related decline in these outcomes was similar in women and in men. In the cortex, porosity (Ct.Po) was 31% to 44% lower in young women than in young men but increased 92% to 176% more with age in women than in men (p < .001). The DR cortex carried 14% more load in young women than in young men, and the percentage of load carried by the DR cortex did not change with age in women but declined by 17% in men (p < .01). FEA-estimated bone strength was 34% to 47% greater in young men, but the predicted change with age was similar in both sexes. In contrast, the load-to-strength ratio increased 27% more in women than in men with age (p < .01). These results highlight important site- and sex-specific differences in patterns of age-related bone loss. In particular, the trends for less periosteal expansion, more porous cortices, and a greater percentage of load carried by the DR cortex in women may underpin sex differences in forearm fracture risk. © 2011 American Society for Bone and Mineral Research.