The structure and morphology of nylon 4 chain-folded lamellar crystals has been investigated using TEM, selected area electron diffraction, and X-ray diffraction. Solution-grown crystals are seen in the electron microscope in the form of sheaves with lathlike extremities. Electron diffraction patterns show the 0.44 (200) and 0.37 nm (020) reflections which are representative of the interchain distance within a hydrogen-bonded sheet and the intersheet distance, respectively, and are characteristic of the broader family of polyamides. The orientation of the electron diffraction patterns from individual lamellar crystals establishes that the polymer chains lie perpendicular to the lamellar surface and that the folding plane is parallel to the long axis of the crystal