Equilibrium structures and harmonic vibrational frequencies were computed for adamantane (Ad), the 1- and 2-adamantyl radicals (1-Ad(.) 2-Ad(.)), cations (1-Ad(+), 2-Ad(+)), and anions (1-Ad(-), 2-Ad(-)). Ionization potentials and electron affinities of Ad, 1-Ad(.) and 2-Ad(.) have been predicted using four different density functional and hybrid Hartree-Fock/density functional methods. The equilibrium structure of adamantane (T-d symmetry) is in excellent agreement with electron diffraction experiments. 1-Ad(.) and 1-Ad(-) are predicted to lie about 4 0 mol(-1) below their 2-isomers, while 1-Ad(+) is predicted to lie 47 kJ mol(-1) below 2-Ad(+). For 1-Ad(.), 1-Ad(+), and 1-Ad(-), C-3upsilon structures are found to be the minima, while a C-s structure lies lowest for 2-Ad(.), 2-Ad(+), and 2-Ad(-). The final predicted adiabatic ionization potentials for the radicals are 6.22 (1-Ad(.)) and 6.70 eV (2Ad(.)). The vertical radical ionization potentials are necessarily larger: 6.85 (1-Ad(.)) and 7.08 eV (2-Ad(.)). The predicted adiabatic electron affinities are all negative: -0.13 (1-Ad(.)) and -0.13 eV(2-Ad(.)). The vertical electron affinities are -0.28 (1-Ad(.)) and -0.37 eV(2-Ad(.)). The vertical detachment energies are 0.07 (1Ad(-)) and 0.22 eV(2-Ad(-)).