The effect of a magnetic field on any crystalline material is to introduce an anisotropy in the electric resistivity. This letter examines the anisotropy which appears in the (001) plane of cubic crystals. Compact formulas are developed which show that in general the extreme values of the resistivity occur in directions which differ from those of the crystallographic axes. We thus demonstrate the existence of magnetoresistance skewness, as defined in recent papers of Allgaieretal., but have analyzed the phenomenon from a point of view which is complementary to that employed in the earlier work.