A microwave radiative transfer model that describes the effect of scattering by cirrus clouds on the brightness temperatures that may be measured by a geostationary temperature-sounding radiometer has been developed. The model assumes that cirrus clouds are situated at an altitude where the temperature is ~230 K above completely absorbing land surfaces. It is shown that the brightness temperature at 118.75¿3.9 GHz is depressed by 0.3--0.4 K g-1 m-2 of ice. The channels that operate at frequencies closer to 118.75 GHz are less affected by cirrus clouds. The brightness temperate reduction is most pronounced in warm temperature and tropical conditions. ¿ American Geophysical Union 1988