Creatininium hydrogen maleate.

In the title compound, C4H8N3O+·C4H3O4−, the cations and anions are linked through N—H⋯O hydrogen bonds making a ionic pair with an R22(8) ring motif. These ionic pairs are further connected through another N—H⋯O hydrogen bond, leading to an R66(16) ring motif around the inversion centres of the unit cell. These approximately planar aggregates are further connected through weak van der Waals inter­actions in the unit cell. The anions have a characteristic intra­molecular O—H⋯O hydrogen bond with a self-associated ring S(7) motif.