Two salts of 1,9-di-hydro-purin-6-one (hypoxanthine), namely, 6-oxo-1,9-di-hydro-purin-7-ium 5-sulfosalicylate dihydrate, C5H5N4O+·C7H5O6S-·2H2O, (I), and 6-oxo-1,9-di-hydro-purin-7-ium perchlorate monohydrate, C5H5N4O+·ClO4 -·H2O, (II), have been synthesized and characterized using single-crystal X-ray diffraction and Hirshfeld analysis. In both salts, the hypoxanthine mol-ecule is protonated at the N7 position of the purine ring. In salt (I), the cation and anion are connected through N-H⋯O inter-actions. The protonated hypoxanthine cations of salt (I) form base pairs with another symmetry-related hypoxanthine cation through N-H⋯O hydrogen bonds with an R 2 2(8) ring motif, while in salt (II), the hypoxanthine cations are paired through a water mol-ecule via N-H⋯O and O-H⋯N hydrogen bonds with an R 3 3(11) ring motif. The packings within the crystal structures are stabilized by π-π stacking inter-actions in salt (I) and C-O⋯π inter-actions in salt (II). The combination of several inter-actions leads to the formation of supra-molecular sheets extending parallel to (010) in salts (I) and (II). Hirshfeld surface analysis and fingerprint plots reveal that O⋯H/H⋯O contacts play the major role in the crystal packing of each of the salts, with a 54.1% contribution in salt (I) and 62.3% in salt (II).