The pyrimidinone ring in the title compound, C(12)H(13)N(5)O(3), is effectively planar, despite the presence of five substituents. The bond distances provide evidence for significant polarization of the electronic structure, with charge separation, and the molecules are linked into sheets by a combination of N-H...O and N-H...pi(arene) hydrogen bonds. Comparisons are made with the molecular and supramolecular structures of the precursor compound 2-amino-6-[methyl(phenyl)amino]-5-nitropyrimidin-4(3H)-one.