In the upper stratosphere the atmosphere exhibits significant diurnal and semidiurnal tidal variations with typical amplitude of about 2 K in midlatitudes. In this paper we examine how well the tidal variations in temperature are represented by the GEOS-2 data assimilation system. It is shown that the GEOS-2 atmospheric model is quite successful at simulating the tidal variations. However, the assimilation of satellite temperature soundings significantly damps the simulated tides. The reason is that the tides are not well represented by the satellite retrievals used by the assimilation system (which have a typical tidal amplitude of about 1 K). As a result of this study, we suggest improvements that should be made to the treatment of satellite sounding data by the assimilation system. ¿ 1999 American Geophysical Union