Using a large, polarized basis set, SCF and MP4 calculations of the previous termstructure and binding energy of the coppernext term(I) - carbon monoxide complex have been calculated. Both carbonyl (Cu+-CO) and isocarbonyl (Cu+-OC) coordination modes have been found to correspond to minima on the potential previous termenergynext term profiles, the Cu+-CO species being more stable at the MP4 level by 15.7 kcal/mol. A decomposition of the interaction previous termenergiesnext term according to the procedure suggested by Morokuma allows to conclude that Cu+-CO is a typical polarization complex, whereas Cu+-OC has a predominant electrostatic character.