The structures and stabilities of CH52+ and CH62+ and their isoelectronic boron analogues BH52+ and BH63+, respectively, were calculated at the MP2/6-31G** and QCISD (T)/6-311G** levels. The planar D-5h symmetric structure 3 is a minimum for the CH53+ trication. The five hydrogens in structure 3 are bonded to the carbon atom by sharing the six valence electrons. Calculations showed that the CH04+ tetracation does not correspond to a minimum at the levels studied. The planar C-2x symmetric structure 6, with two 3c-2e (three-center two-electron) bends, on the other hand, was found to be a minimum for the BH52+ dication. The D-j symmetric structure 8 also corresponds to a stable minimum for the BH63+ trication.