The title compound, C(13)H(8)Cl(2)N(2)O(2), was obtained by the oxidation of diclofenac {systematic name: 2-[2-(2,6-dichloro-phenyl-amino)-phen-yl]acetic acid}, an anti-inflammatory drug, with hydrogen peroxide catalysed by chlorido[5,10,15,20-tetra-kis-(2,6-dichloro-phen-yl)porphyrinato]manganese(III), using ammonium acetate as co-catalyst. The asymmetric unit contains two crystallographically independent mol-ecules of the title compound (Z' = 2). The close packing of individual mol-ecules is mediated by a series of strong and rather directional N-H⋯Cl and N-H⋯O hydrogen bonds, plus weak π-π [distance between the individual double bonds of symmetry-related imino-quinone rings = 3.7604 (13) Å] and Cl⋯O inter-actions [3.0287 (18) Å].