We report InSAR observations of coseismic ground deformation caused by the Mw6.4 Chamoli earthquake of March 28, 1999 in the western Himalaya near the surface trace of the Main Central Thrust. Analysis of ERS1/2-SAR data from ascending and descending tracks reveals surface deformation in a region 30 km by 40 km with a maximum coseismic uplift of ~60 mm. Assuming that the rupture occurred as a planar uniform slip dislocation in an elastic half space reveals slip of 0.55 ¿ 0.1 m, strike of N300¿E, 15¿ dip, with fault dimensions of 13 ¿ 3 km along-strike and 10 ¿ 3 km downdip. The corresponding moment magnitude is Mw = 6.2, lower than that derived from seismological methods. With the exception of the recent 2005 Kashmir earthquake, the Chamoli earthquake studied in this paper is the only Himalayan earthquake for which surface deformation data are available from directly above the epicenter.