Changes in the surface morphology and optical transmittance of polymers, poly(methyl methacrylate) (PMMA) thin films on quartz glass plates and poly(tetrafluoroethylene) (PTFE) sheets, induced by megaelectronvolt ion implantation, were examined using different ion species, energies, ion current densities and doses. The polymer surface showed remarkable depression after ion implantation. On PMMA, the depression increased with dose and saturated after a dose of about 5 x 10(14) ions cm(-2). Higher energy and heavier ions made a larger depression generally. On PTFE, implantation of heavy ion species made a small depression and the dependence on dose was almost linear in the range 10(14) to 10(15) ions cm(-2). PMMA changed its appearance from transparent to white, light brown, brown and finally black with dose, because of UV-visible light absorption. The width of the absorption band increased with dose, and the implantation of heavier ion species caused wider and larger absorption. Some annihilation of light absorption with time was found at room temperature. Roughening of the ion implanted surface was also observed.