A numerically manageable formalism for the dynamical calculation of diffuse reflection high-energy electron diffraction (RHEED) is presented. The diffuse scattering arises from transitions between dynamically calculated scattering states in the periodic part of the scattering potential and the nonperiodic part is treated as a perturbation. For atoms placed on equivalent lattice sites relative to the periodic-potential part, the formalism allows us to treat disorder scattering by kinematical structure factors that have to be multiplied by dynamically calculated atomic-scattering amplitudes so that the statistics of the disorder can be treated independently of the dynamical calculations