Small-angle X-ray scattering was used to compare the morphology of extruded ultrahigh molecular weight polyethylene (UHMWPE) and melt-crystallized high-density polyethylene (HDPE). The crystalline morphology of UHMWPE has a low degree of order, rendering direct methods of analysis of the scattering curves unsuitable. We have demonstrated that the indirect transformation method, requiring no extrapolation of the scattering curve, can be used to obtain the one-dimensional correlation functions for these dense lamellar systems. The lamellar morphology of UHMWPE contained a large distribution of lamellar thicknesses, diffuse interfaces, and a large variation of interlamellar spacing as compared to those features in HDPE. The interlamellar spacing of extruded UHMWPE determined from the one-dimensional correlation function was 50 nm and that of melt-crystallized HDPE was 26 nm. The amorphous zone thickness of HDPE was 8 nm.