The theory of inelastic scattering of fast electrons in the case of large-angle single scattering is developed on the basis of the generalized model of continuous losses. The angular and thickness dependence of the inelastic scattering coefficient and the energy spectrum of the inelastically backscattered electrons are established. Measurements of the inelastic coefficient are made as a function of the electron angle of incidence and the film thickness. From a comparison of the theoretical and experimental data it is concluded that the model correctly describes the mechanism of the scattering of electrons in thin films. (auth)