Proximal femoral dimensions were measured from radiographs of 80 living subjects whose current body weight and body weight at initial skeletal maturity (18 years) could be ascertained. Results generally support the hypothesis that articular size does not change in response to changes in mechanical loading (body weight) in adults, while diaphyseal cross-sectional size does. This can be explained by considering the different bone remodeling constraints characteristic of largely trabecular bone regions (articulations) and largely compact cortical bone regions (diaphyses). The femoral neck shows a pattern apparently intermediate between the two, consistent with its structure. When the additional statistical “noise” created by an essentially static femoral head size is accounted for, the present study supports other studies that have demonstrated rather marked positive allometry in femoral articular and shaft cross-sectional dimensions to body mass among adult humans. Body weight prediction equations developed from these data give reasonable results for modern U.S. samples, with average percent prediction errors of about 10%–16% for individual weights and about 2% for sample mean weights using the shaft dimension equations. When predicting body weight from femoral head size in earlier human samples, a downward correction factor of about 10% is suggested to account for the increased adiposity of very recent U.S. adults.