The vertical roughness of the martian surface at ~250 m spatial scales has been determined in two global latitude bands: an equatorial and a high northern band acquired from 18 tracks of data by the Mars Orbiter Laser Altimeter (MOLA) during the Fall of 1997. The distribution of RMS vertical roughness, as derived from MOLA pulse widths, for the equatorial band is non-gaussian, with an overall mean of 2.8 m RMS, but with secondary populations at 1.5 m and 2--6 m RMS. The higher latitude northern plains of Mars are almost uniformly ~1 m RMS in their vertical roughness characteristics, suggesting that they are smoother than virtually any terrestrial deserts. We suggest that dust mantling has muted the local topography of Mars, rendering it as smooth as 1--2 m RMS. Heavily cratered uplands near the martian equator are noticeably rougher, indicating more rugged and less-mantled local topography. ¿ 1999 American Geophysical Union