The crystalline morphology and the orientation in thin films of polyamide-6 crystallized on polystyrene- or ethylene-propylene-diene rubber-coated silicon substrates were analysed by transmission electron microscopy (TEM), X-ray and electron diffraction. Bright-field TEM imaging of thin films demonstrated that lamellae organize into disc-shaped crystals, or ’discoids’, when the film thickness is below 0.5 mu m. A model is presented for the organization of lamellae and the polyamide-6 chains in the lamellae of the discoids. In the inter-discoid regions, the films are semicrystalline and the lamellae fill the space randomly. Orientation studies by means of electron diffraction and wide-angle X-ray scattering showed that in relatively thin films (<0.5 mu m) the (0 0 2) hydrogen-bonded planes are parallel to the surface of the film. This orientation gradually diminishes as the film thickness increases. The change in orientation affects the mechanical properties : under uniaxial tension, the modulus and the flow stress of the films increase with decreasing thickness, hence with increasing orientation.