Density functional theory is used to investigate various hydrogenated, dehydrogenated, and hydroxylated radicals formed upon irradiation of adenine. The relative energies, geometries, and hyperfine coupling constants of possible radicals are discussed. The hyperfine couplings are compared to experimental data in order to confirm the assignment of particular couplings to specific radicals. The C8-hydrogenated and the N9-dehydrogenated radicals are the lowest energy radicals in their respective classes. Several degrees of geometrical distortion are exhibited in the adenine radicals. For example, the C2- and C8-hydrogenated radicals are only slightly distorted, whereas the C4- and the CS-hydrogenated radicals are severely puckered. Several N1-protonated radicals are also examined. In particular, the differences in the HFCCs for the various protonated forms of the C2- and the C8-hydrogenated radicals are well described by an appropriate level of density functional theory.