To identify the racial differences in macro- and microstructure of the distal radius and tibia that may account for the lower fracture rates in Asians than whites, we studied 61 healthy premenopausal Chinese and 111 white women 18-45 yr of age using high-resolution pQCT (HR-pQCT). The Chinese were shorter and leaner. Distal radius total cross-sectional area (CSA) was 14.3% smaller in Chinese because of an 18.0% smaller trabecular area (p < 0.001). Cortical thickness was 8.8% greater in the Chinese, but cortical area was no different. Total volumetric BMD (vBMD) was 10.3% higher in the Chinese because of the 8.8% higher cortical thickness and 2.8% greater cortical density (all p < 0.01). Trabecular vBMD and bone volume/tissue volume (BV/TV) did not differ by race because trabeculae were 7.0% fewer but 10.8% thicker in Chinese than whites (both p < 0.01). Similar results were found at the distal tibia. Lower fracture risk in Chinese women may be partly caused by thicker cortices and trabeculae in a smaller bone-more bone within the bone than in whites.