IN THE TITLE SALT (SYSTEMATIC NAME: 6-amino-9H-purin-1-ium perchlorate), C(5)H(6)N(5) (+)·ClO(4) (-), the adeninium cation is essentially planar, with a maximum deviation of 0.038 (1) Å. The whole of the perchlorate anion is disordered over two sets of sites with an occupancy ratio of 0.589 (13):0.411 (13). In the crystal, the adeninium cations are linked by pairs of N-H⋯N hydrogen bond into inversion dimers. The dimers and the anions are further inter-connected into a three-dimensional supra-molecular structure via inter-molecular N-H⋯O, C-H⋯O and C-H⋯N hydrogen bonds.