Small angle X-ray scattering (SAXS) functions of various distorted multilayers (MLs) are presented. The following structural modifications are treated here : the finiteness of the ML structure, the paracrystalline distortion, the layer-thickness distribution, the layer curvature, the formation of the transitional zone at the interface, and the electron-density fluctuation. For each defect, the characteristic features of the SAXS patteRN are elucidated. The methodology of the precise structural characterization of MLs by SAXS is proposed, and its applicability and limitations are discussed.