Single pixel, tropospheric retrievals of HDO and H2O concentrations are retrieved from Atmospheric Infrared Sounder (AIRS) radiances using the optimal estimation algorithm developed for the Aura Tropospheric Emission Spectrometer (TES) project. These retrievals are evaluated against co-located TES observations taken between 2006 through 2010. We evaluate the error characteristics and vertical sensitivity of AIRS measurements corresponding to five days of TES data (or 5 global surveys) during the N. Hemisphere summers between 2006 and 2010 (~600 co-located comparisons per day). We find that the retrieval characteristics of the AIRS deuterium content measurements have similar vertical resolution and uncertainty in the middle-troposphere as TES but with slightly less sensitivity in the lower-most troposphere, with a typical degrees-of-freedom (DOFS) in the tropics of 1.5. The difference in sensitivity to the lower-most troposphere is mostly likely due to the reduced spectral resolution as previous studies found that spectral resolution was the primary factor, relative to signal-to-noise, affecting the vertical resolution of nadir sounding retrievals (Worden et al., 2004). The calculated measurement uncertainty is ~30 per mil (parts per thousand relative to the deuterium composition of ocean water) for a tropospheric average between 750 and 350hPa, the altitude region where AIRS is most sensitive. Comparison with the TES data suggest that the calculated and actual uncertainty of a single target AIRS HDO/H2O measurement ~30 per mil. Comparison of AIRS and TES data between 30S and 50N suggest that the AIRS data is biased low by ~−2.6 per mil with a latitudinal variation of ~7.8 per mil. This latitudinal variation is consistent with the accuracy of TES data as compared to in situ measurements, suggesting that both AIRS and TES have similar accuracy. [ABSTRACT FROM AUTHOR]