The OMEGA imaging spectrometer aboard Mars Express has been used to map the water vapor abundance over the martian surface, from the analysis of the 2.6 μm band of H 2 O. As a preliminary result of this study, we present water vapor maps in the northern hemisphere at the time of the northern polar cap sublimation (Ls = 94-112 deg). The maps show a mean H 2 O mixing ratio of about 2-3 x 10 -4 at a latitude of 40N, and in the range of 5 x 10 -4 -10 -3 at 60N-80N latitudes. The corresponding mean H 2 O column densities are about 25 pr-μm at 40N and between 40 and 60 pr-μm at 60N-80N, with uncertainties of about 30 percent. Our results are in agreement with previous results by MAWD/Viking and TES/MGS for latitudes up to 60N, but seem to indicate lower values at high latitude. However they are still globally consistent in view of our error bars.