The geometry and electronic structure of group 10 and I I metal carbonyl cations, [M(CO)(n)](x+) (Mx+ = Ni2+, Pd2+, Pt2+, Cu+, Ag+, Au+; n = 1-4), were examined by the hybrid density functional method (B3LYP) and the coupled cluster method (CCSD(T)). For group 10 metals, monocarbonyl cations have C, structures, dicarbonyl cations have D-infinityh and C-2v structures, and tri- and tetracarbonyl cations have C-2v and D-4h structures, respectively. Group 11 metal carbonyl cations have C-infinityv, D-infinityh, D-3h, and T-d structures for mono-, di-, tri-, and tetracarbonyls, respectively. The (CO)(n-1)Mx+-CO dissociation energies Do (CO) of group 10 metal carbonyl cations are significantly larger than those of group 11 metal carbonyl cations. Group 10 metal tetracarbonyl cations are still stable, while for group 11 metals, Do (CO) is significantly reduced in going from dicarbonyls to tri- and tetracarbonyls. The vibrational frequencies v(CO) are higher by 110-165 cm(-1) for group 10 metal complexes and by 45-115 cm(-1) for group 11 metal complexes than that for free CO (2143 cm(-1)).