The axes of the maximum moment of inertia of recent three-dimensional models of the Earth deviate from the rotation axis by about one degree. This is at least a few orders of magnitude larger than the observed deviation. Simple analysis shows that this is related to the size of the (l=2,m=1) component of density variations in the upper mantle, where l is the angular degree and m is the order of the spherical harmonics. An analytical formula for the deviation of the maximum moment of inertia is derived, which involves a radial integration of the (l=2,m=1) component of density. It is proposed that a new Earth model should be derived using this constraint. ¿ American Geophysical Union 1989