Fenton-like oxidation has proved to be highly efficient in the degradation of polychlorinated phenols (poly-CPs) at 50 degrees C provided that the H2O2 dose is adjusted appropriately. Using the theoretical stoichiometric H2O2/poly-CP molar ratio allowed a high mineralization of the starting poly-CPs, with negligible residual concentrations of chlorinated organic species and a dramatic reduction of ecotoxicity. Nevertheless, at substoichiometric H2O2 doses, a wide variety of chlorinated condensation byproducts (chlorinated diphenyl ethers, biphenyls, and dibenzofurans) were detected. A chlorinated aromatic iron-containing solid polymer was also formed. At these substoichiometric H2O2 doses, the ecotoxicity values even increased with respect to those of the starting poly-CPs. A reaction scheme is proposed to describe the Fenton-like oxidation of poly-CPs that includes all of the intermediates detected under substoichiometric conditions and used to develop a kinetic model based on TOC lumps. This kinetic model describes fairly well the time evolution of TOC upon the Fenton-like oxidation of poly-CPs.