A series of dc magnetron-sputtered Co/Cu superlattices, with Co magnetic layers of ≈ 10 Å thickness and Cu spacer layer thicknesses in the range 10–400 Å, has been characterized by high-resolution electron microscopy. The multilayer structure was found to be polycrystalline with individual columnar grains spanning several bilayers. The grain size increased for Cu spacer layers of greater thickness, with a grain size of at least 3–4 bilayer periods being typical for multilayers with the thickest Cu layers (100–400 Å). In terms of the giant magnetoresistance (GMRC) exhibited by these metallic superlattices, these observations mean that conduction electron scattering at grain boundaries can, to a first approximation, be ignored in models for GMR dependence on Cu layer thickness.