A description of reflection boundaries in x-ray diffraction patterns from oriented and polycrystalline polymer specimens is developed. The description is based on mosaic parameters that characterize the disorientation and crystallite size in the specimen and is independent of the exact reflection shapes. This description is part of a previously described method for measuring integrated intensities from such diffraction patterns. The reliability of the method is assessed using both numerical simulations and measurements from an x-ray fiber diffraction pattern. A method for estimating the mosaic parameters from a diffraction pattern is also described. The relevance to diffraction patterns from non-crystalline oriented polymers is also discussed.