Air pollution control (APC) residues from municipal solid waste incinerator plants that are treated by means of the Ferrox process can be more safely disposed of due to reduction of soluble salts and stabilization of heavy metals in an iron oxide matrix. Further stabilization can be obtained by thermal treatment inside a combustion chamber of a municipal solid waste incinerator. The influence of the Ferrox products on the combustion process, the quality of the residues, and the partitioning of heavy metals between the various solids and the gas have been investigated in the Karlsruhe TAM-ARA pilot plant for waste incineration. During the experiments only few parameters were influenced. An increase in the SO2 concentration in the raw gas and slightly lower temperatures in the fuel bed could be observed compared with reference tests. Higher contents of Fe and volatile heavy metals such as Zn, Cd, Pb and partly Hg in the Ferrox products lead to increased concentration of these elements in the solid residues of the co-feeding tests. Neither the burnout nor the PCDD/F formation was altered by the addition of the Ferrox products. Co-feeding of treated APC residues seems to be a feasible approach for obtaining a single solid residue from waste incineration.