I attempted to find basic bone morphology and bilateral asymmetry for the human paired radii based on intra-regional and side ratios for a total of 11 length, width, depth and girth measurements. Four hundred and seventy paired radii of Iraqis, Germans and Japanese were used for this purpose.The maximum bone length and 6 intra-regional ratios of the radius for Iraqis and Japanese exhibited significant sexual dimorphism in bone morphology, while the maximum bone length and 6 intra-regional ratios for Iraqis and Japanese of both sexes, as well as German males, also showed significant ethnic differences. On the other hand, the maximum bone length and 10 intra-regional ratios from the paired radii did not exhibit any significant side differences in bilateral asymmetries, although all of them showed significant side correlations. In addition, four side ratios for the bone length, and the robustness of the midshaft and distal end, exhibited significant sexual dimorphism and ethnic differences. On the basis of these results, the interrelations of basic, adaptive and bilateral bone morphology for the human paired radii were viewed in terms of bone growth and remodelling, biomechanics, cooperative use of the paired upper limbs, and differences in intrinsic and extrinsic factors for the Iraqis, Germans and Japanese.