We validate the temperature climatology recorded by the Microwave Sounding Unit with GPS occultation data collected by the GPS/MET experiment. We choose to validate only the lower stratospheric MSU climatology in order to circumvent the wet-dry ambiguity associated with GPS occultation in the mid- to lower troposphere. We simulate the lower stratospheric channel's brightness temperature by convolving each GPS/MET temperature profile with a vertical weighting function and then map the irregularly gridded data using a Bayesian interpolation scheme. In northern polar night, the MSU Tls deviates from GPS occultation by as much as 10 K while occultation is consistent with the NCEP Reanalysis used for diagnostic purposes. NCEP and GPS occultation deviate by 1 K in the tropics, consistent with a warm bias in NCEP Reanalysis. GPS occultation renders the problems MSU encounters with inter-satellite calibration obsolete, because calibration by atomic clocks is free of systematic error and can completely cover the diurnal cycle.