Racial/ethnic origin plays an important role in fracture risk. Racial/ethnic differences in fracture rates cannot be fully explained by bone mineral density (BMD). Studies examining the influence of bone geometry and strength on fracture risk have focused primarily on older adults and have not included people from diverse racial/ethnic backgrounds. Our goal was to explore racial/ethnic differences in hip geometry and strength in a large sample of midlife women. We performed Hip Structure Analysis (HSA) on hip DXA scans from 1942 pre- and early peri-menopausal women. The sample included Caucasian (50%), African American (27%), Chinese (11%) and Japanese (12%) women, age 42-52 years. HSA was performed using software developed at John’s Hopkins University. African American women had higher conventional (8.4-9.7%) and HSA BMD (5.4-19.8%) than other groups with the exception being Japanese women who had the highest HSA BMD (9.7-31.4%). HSA indices associated with more favorable geometry and greater strength and resistance to fracture were more prevalent in African American and Japanese women. Femurs of African American women had a smaller outer diameter, a larger cross-sectional area and section modulus, and a lower buckling ratio. Japanese women presented a different pattern with a higher section modulus and lower buckling ratio, similar to African American women, but a wider outer diameter; this was offset by a greater cross-sectional area and a more centrally located centroid. Chinese women had similar conventional BMD as Caucasian women but a smaller neck region area and HSA BMD at both regions. They also had a smaller cross-sectional area and section modulus, a more medially located centroid, and a higher buckling ratio than Caucasian women. The observed biomechanical differences may help explain racial/ethnic variability in fracture rates. Future research should explore the contribution of hip geometry to fracture risk across all race/ethnicities. (c) 2012 American Society for Bone and Mineral Research.