The title organic salt, C(4)H(6)N(3)O(+)·C(4)H(3)O(4) (-)·C(4)H(5)N(3)O, was synthesized from cytosine base and maleic acid. An intra-molecular O-H⋯O hydrogen bond occurs in the hydrogen maleate anion. The crystal packing is stabilized by inter-molecular N-H⋯O, N-H⋯N and C-H⋯O hydrogen bonds, giving rise to a nearly planar two-dimensional network parallel to (101).