In the title mol-ecule, C(12)H(11)N(3)O(2), the dihedral angle between the mean planes of the naphthalene and carboxamide groups is 28.9 (8)°. The hydrazine N atoms are twisted slightly out of the plane of the carboxamide group [C-C-N-N torsion angle = -175.06 (13)°]. The crystal packing is influenced by N-H⋯O hydrogen bonding which includes a bifurcated hydrogen bond between the amide N atom and nearby carboxyl and hydroxyl O atoms. A second bifurcated hydrogen bond occurs between the hydroxyl O atom and nearby amide (inter-molecular) and hydrazine (intra-molecular) N atoms. As a result, mol-ecules are linked into a co-operative hydrogen-bonded network of infinite one-dimensional O-H⋯O-H⋯O-H chains along the (101) plane of the unit cell in a zigzag pattern, the dihedral angle between the mean planes of the naphthalene groups of adjacent mol-ecules in the chain being 86.9 (2)°. A MOPAC PM3 calculation provides support to these observations.