High level ab initio calculations are performed on the Ar . NO+ complex to ascertain its geometric structure. The calculations show that the complex is bent, with an Ar-N-O angle of similar to 105 degrees, i.e. the argon atom is on the nitrogen side of the complex cation. Calculations are performed with the cc-pVDZ and cc-pVTZ basis sets at the MP2, MP4(SDQ), QCISD, CISD, CCSD(T), and QCISD(T) levels of theory; in addition the hybrid density functionals BLYP, B3LYP, and BPW91 are used. Harmonic vibrational frequencies are also calculated for all except the two highest levels of theory, but it is recognized that the surface is anharmonic and these are not good estimates of the vibrational separations; however, by comparison with the ab initio results, they demonstrate that these density functional methods are not trustworthy for this complex.