The title mol-ecule, C(17)H(13)N(5)O(4)S, has a trans configuration with respect to the diazenyl (azo) group. The pyrimidine ring and the terminal benzene ring are inclined at angles of 89.38 (4) and 1.6 (6)°, respectively, with respect to the central benzene ring. The conformation of the mol-ecule is in part stabilized by an intra-molecular O-H⋯O hydrogen bond. In the crystal structure, mol-ecules related through inversion centers form hydrogen-bonded dimers involving the sulfon-amide N-H group and the N atom of the pyrimidine ring.