Osteoporosis affects all populations, but the risk for low bone density and fracture varies greatly by self-reported race and ethnicity. In this article, the relationship between measured percent African admixture and hip structural geometry, estimated from the hip structural analysis (HSA) program, was examined in a subcohort of the Women's Health Initiative (WHI). The study sample included 793 African-American women and 8559 non-Hispanic white women. All the participants were postmenopausal, between the ages of 50 and 79 years, at the time of recruitment and were followed for up to 9 years. Bone density and hip geometry were assessed using dual-energy X-ray absorptiometry. African admixture was measured for African Americans using genetic ancestry informative markers. Multiple regression and mixed-effects models were used for cross-sectional and longitudinal analyses, respectively. Covariates assessed from questionnaires and physical measurements were included in the analysis to control for possible confounding effects. The study results show significant correlations between percent of African admixture and HSA assessments. In comparison with non-Hispanic white women, significantly greater bone strength, as indicated by higher hip bone mineral density and stronger hip geometry, in women with higher African admixture was observed. However, women with higher percent African admixture had larger reductions in bone strength than non-Hispanic white women during the follow-up. © 2011 American Society for Bone and Mineral Research.