The cationic complex formed between NO+ and CO is investigated using high-level ab initio calculations. Geometries were optimized rat at the MP2/6-31+G* and then the MP2/aug-cc-pVTZ level of theory. At the latter level all linear isomers were found to be transition states. Two minima were found, corresponding to skewed structures. Finally the relative energies were calculated at the CCSD(T)/aug-cc- pVQZ//MP2/aug-cc-pVTZ level of theory, correcting for basis set superposition error. The binding energy of the lowest energy isomer was calculated to be 2730 cm(-1). Finally, density functional theory (DFT) methods were concluded to overestimate the interaction.