A highly crosslinked amorphous polymer is produced by passing ethylene through a radio-frequency electric discharge. The morphology of plasma-polymerized ethylene is examined by replica electron microscopy. It is found that at low pressures and flow rates spherical powder particles are formed ranging in size between 0.2 and 1.2 μm. At high pressures and flow rates a film is formed. The role of the substrate on which the polymer is deposited has been investigated using chromium, Teflon, glass, and freshly cleaved mica as substrates. These materials are listed in order of increasing smoothness. From the electron micrographs it is observed that the surface structure of the substrate is reproduced in the plasma-polymerized films as long as the film is thin ([inverted lazy s] 0.5 μm). Thicker films produced by a longer exposure to the ethylene plasma are characterized by a surface which is smoother than that of the substrate.