Calibrated pores in the range 102–2×103 Å have been obtained by chemical etching of polycarbonate thin films irradiated with high energy krypton ions (500 MeV, Kr25+). Both the amorphous and the crystalline forms of polycarbonate (Makrofol, Bayer), further designated by their respective trade names N and KG, have been investigated up to thicknesses of 60 μm, close to the theoretical ion range of 77 μm. From conductivity studies, three different domains have been separated around the ion track: A highly damaged core of radius ?50 Å with a fast etching rate vT ≊104 Å/min, an intermediate zone of radius ?500 Å with an etching rate vI = 0.9 Å/min, an outer region with an etching rate equal to that of the undamaged material, vG = 0.47 Å/min. These observations are compatible with the delta ray model for track formation in plastic materials. Scanning electron microscope investigations have revealed that the pores formed in the N material are straight cylinders with a narrow distribution of the pore entrance diameters. On the other hand, the pores for the KG type are much less uniform and appear to be tapered, the difference between the two sides of the membrane being as much as 50%. These characteristics could be related to inhomogeneities in the morphological structure due to (i) the finite size of the crystalline domains and (ii) an asymetric manufacturer’s processing of the film surfaces.