Density functional calculations (B3LYP/6-31G(d)) are presented for the anion and radical of the monocarbon carboranes, CBnHn+1, n = 4, 9, 11. The CB4H5-, CB9H10-, and CB11H12- anions, which are isoelectronic with the closo-dicarba species C2B3H5, C2B8H10, and C2B10H12, are predicted to have significant ionization potentials (2.88, 4.36, and 5.19 eV). The recently reported synthesis of the permethyl derivative of the CB11H12 radical is remarkable in view of the large predicted ionization potential of the CB11Me12- anion (4.32 eV). All calculated properties are consistent with the removal of an electron from a cage-bonding orbital with significant unpaired spin density on the boron opposite the carbon vertex.