The coherence method, based on the statistical correlation between gravity and topography, has been widely used to estimate the effective elastic thickness of the continental lithosphere and its variations. By far the majority of studies have assumed an isotropic lithosphere, but several papers have inferred anisotropy from differences in the observed coherence (or admittance) functions in different directions. However, none have used an anisotropic model to fit the coherence. We show how the simplest model of elastic anisotropy (an orthotropic thin plate) can be incorporated into both forward and inverse modeling algorithms, using an appropriate approximation in the partial differential equation for the flexure of such a plate.