We examine simulations of the surface mass balance of the sector of the East Antarctic Ice Sheet between 2.4 ¿W and 110.5 ¿E as produced by the United Kingdom Meteorological Office Unified Climate Model. Estimates of the actual mass balance of this sector can be obtained from glaciological observations of snow accumulation and from studies of the atmospheric water vapor budget using radiosonde observations. The former technique gives an average sector accumulation of 104 mm yr-1, and the latter yields 157 mm yr-1. The modeled accumulation in this sector, 122 mm yr-1, lies between these two estimates, suggesting that the model can accurately represent the processes controlling surface mass balance. However, examination of the atmospheric water vapor budget in the model shows that only 30% of the water vapor precipitated in this sector is carried by resolved-scale transport. Although the model produces the ''correct'' accumulation in present-day climate simulations, it is not clear that this would change appropriately if the model were used to simulate future climates. By producing synthetic estimates of water vapor transport at radiosonde station locations we have used the model data to investigate the uncertainties in estimating sector accumulation from radiosonde data. The results of this study indicate that the radiosonde technique will tend to overestimate sector accumulation, thus reconciling the two observational estimates. ¿ American Geophysical Union 1996