Very thin sputtered Mo films (thicknesses < 800 Angstrom) have been investigated in order to gain a better understanding of the relationship between the development of microstructure, morphology and residual stress. Mo films were grown by planar magnetron sputtering (3 mTorr Ar) onto Si substrates with native oxide. Examination of a large number of Mo films using double crystal diffraction topography showed that a large compressive stress (similar to 1 GPa) was accumulated in the thinnest films studied (similar to 33 Angstrom). The film stress relaxed with increasing thickness and eventually crossed over to the tensile regime. The microstructure of these films have been studied using two techniques, transmission electron microscopy and grazing incidence X-ray scattering. The evolution of microstructure in Mo films has been examined by monitoring the in-plane grain size as a function of him thickness, beginning with 33 Angstrom thick films. Both techniques showed that the grain width increased rapidly at the earliest stages of growth, but exhibited a slower increase in growth by thicknesses similar to 800 Angstrom.