The Geostationary Earth Radiation Budget (GERB) instrument on the Meteosat Second Generation (MSG) satellite is dedicated to the accurate measurement of the energy fluxes of the reflected solar radiation and of the emitted thermal radiation at the Top Of the Atmosphere (TOA). The error on the TOA fluxes is dominated by the uncertainty on the Angular Dependency Models (ADM’s) that are used to convert the directional GERB radiances into hemispherically integrated fluxes. We validate the emitted thermal GERB TOA fluxes by comparing them with colocated fluxes from the Clouds and Earth’s Radiant Energy System (CERES) instruments on the polar Terra and Aqua satellites. For a given location on earth and a given time of day, the GERB viewing geometry is fixed, while the CERES viewing geometry is variable. Hence the statistical comparison of GERB and CERES fluxes yields a direct estimation of the GERB TOA flux accuracy.