This work deals with the analysis of the applicability of the approximate theory of the dielectric response of colloidal suspensions elaborated by Fixman (J. Chem. Phys. 78, 1483 (1983)) for particles with thin double layers, The predictions of this, comparatively simple, analytical model are compared, for a wide range of the variables of interest, with exact numerical results computed according to DeLacey and White’s standard theory (J. Chem. Sec. Faraday Trans. 2 77, 2007 (1981)). The interest of this comparison lies in the possibility of delimiting to what extent the thin double-layer approximation agrees with the standard model, since new theories, incorporating ionic transport in the inner part of the double layer, have been proposed to explain well-documented discrepancies between theoretical and experimental data on the dielectric behavior of suspensions, Some such models are generalizations of Fixman’s theory, and once the true limits of validity of the latter are established, it will be possible to ascribe the possible differences between measurements and predictions to actual physical facts rather than to errors bound by the use of approximate analytical solutions outside their range of validity.