1] Martian high latitudes have thermal properties consistent with an extensive high thermal inertia permafrost layer near the surface. Surface cover thermal inertias and permafrost depths at Martian high latitudes (50°–80°N/S) are derived from Thermal Emission Spectrometer (TES) data and compared with previously published water ice depths determined from the Mars Odyssey Neutron Spectrometer (MONS). The depth to the permafrost layer is correlated with surface cover thermal inertia, albedo, and latitude in general agreement with predicted trends of water ice stability. Comparison of permafrost depths with water ice rich layer depths derived from MONS data displays good qualitative agreement, although a divergence is present at greater burial depths. This disparity may be due to the presence of hydrated minerals at shallow depths or a lower than expected permafrost thermal inertia corresponding with low water ice concentrations at greater depths. Surface cover thermal inertias are greater in the northern high latitudes than in the south and differences between these and previous results will have significant effects on the predicted depth of Martian water ice stability. Several regions in the northern hemisphere display high surface cover thermal inertia associated with possible receding water ice deposits that are shallow enough to influence diurnal surface temperatures. Significant lateral and vertical heterogeneity in water ice distributions are present and the Martian regolith is likely more complicated than can be described by simple two layered models and a single mode of water ice emplacement.