The geometries and the isotropic hyperfine coupling constants of 17 different organic radicals and radical ions were calculated with the use of semiempirical, Hartree-Fock, and density functional methods. A good agreement between the experimental and the theoretical data was found when the geometry of the radical was optimized with density functional methods or the UHF/3-21G* ab initio method, and the Fermi interaction was calculated with the density functionals BLYP/6-31G* or B3LYP/6-31G* at the unrestricted level of theory. This statement holds for all types of radicals studied, i.e. neutral radicals (allyl, bicyclo[1.1.1]pent-1-yl, cubyl, 1,2,3,4,5,6-hexafluorocyclohexadienyl, 2-methyldihydrofuran-4-yl, (PH)-P-.(CH3)(3)), radical cations (norbornadiene, quadricyclane, 1,8-dimethylnaphthalene, acenaphthene, tetramethylhydrazine, 1,2-di(tert-butyl) 1,2-dimethylhydrazine, 1,5-diazabicyclo[3.3.0]octane, 2,3-dimethyl-2,3-diazabicyclo[2.2.1]hept-5-ene), and radical anions (naphthalene, 1,8-dimethylnaphthalene, acenaphthene).