Most long bone fractures are the result of bending and/or torsional loading. To allometrically relate bone torsional and bending strength to animal mass (M), we define the bone strength index S_B = Jdl where J = midshaft cross section polar moment of inertia, d = diameter, and l = length. In geometrically similar scaling, one would expect S_B ∝ M²³. In this study, long bone geometric parameters were measured for 12 species of Artiodactyls. The relationships determined for length and diameter are similar to those reported by previous investigators (l ∝ d³⁴, l ∝ M¹⁴). For the Artiodactyls studied, we found that S_B ∝ M^0.82. Data previously collected by Biewener on a wide range of mammals (non-Artiodactyls) showed different scaling characteristics (l ∝ d^0.89, l ∝ M^0.31). However, our analysis of his data suggests roughly similar scaling of the torsional and bending strength index, S_B ∝ M^0.77. It therefore appears that, in spite of differences in scaling of length and external diameter, the bending and torsional strengths scale similarly across a broad range of animals.