Bouguer gravity and topography data from Tibet suggest that the surface of the plateau and the subsurface density interfaces are warped into two series of ridges and troughs trending parallel to the collision zone with wavelengths of 150 and 500 km. These folds are superimposed on an overall state of isostatic compensation owing to crustal thickening. Such folding is predicted from models of compressional shortening of a theologically layered plate. The results thus suggest the presence of a weak decoupling zone between the Tibetan crust and upper mantle.