In the title compound, C(6)H(10)N(3) (+)·C(7)H(3)N(2)O(6) (-)·2H(2)O, the amino-pyrimidine mol-ecule is protonated at one of the pyrimidine N atoms. The carboxyl-ate group of the 3,5-dinitro-benzoate anion inter-acts with the protonated pyrimidine N atom and the 2-amino group through a pair of N-H⋯O hydrogen bonds, forming an R(2) (2)(8) motif. Two inversion-related pyrimidine rings are linked via a pair of N-H⋯N hydrogen bonds, also forming an R(2) (2)(8) ring motif.