The results of a G2(MP2) computational study involving 1- and 2-Adamantyl cations (1(+),2(+)) as well as 1- and 2-Adamantyl radicals (1(.),2(.)) are presented. They provide purely computational thermodynamic data for the following processes: (i) Ionization of 1(.) and 2(.), (ii) Exchange of hydrogen atoms or hydride anions between Adamantyl radicals or cations and alkyl radicals or cations, respectively. These data, once combined with the experimental enthalpies of formation of iso-C3H7.,iso-C3H7+, tert-C4H9. and tert-C4H9+. allowed us to screen the available experimental data and to define a self-consistent set of experimentally-based standard enthalpies of formation, Delta H-f(m)0. for Adamantyl species, namely: Delta H-f(m)0(1(+),g) = 162.0 +/- 2.0; Delta H-f(m)0(2(+),g) = 171.9 +/- 2.0; Delta H-f(m)0(1(.),g) = 17.9 +/- 2.1, Delta H-f(m)0(2(.),g) = 16.6 +/- 2.0 kcal mol(-1).