In this study, the chemical characterization of solid residues, i.e., bottom ash, fly ash, and filter cake, produced from the Izmit Hazardous and Clinical Waste Incineration Plant (IZAYDAS) was investigated. The IZAYDAS is located in the city of Kocaeli in Turkey and it has been in use since 1997. Several parameters were measured, including AOX, Cl-, CN-, SO42- and selected heavy metals including Pb, Cd, Cr(VI), Cu, Ni, Hg, As(III), and Zn. The results showed that although the temperature and furnace residence time inside the kiln are maintained for complete combustion, cold points and pyrolytic conditions may occur locally and cause the formation of products of incomplete combustion in bottom ash. Fly ash has the highest content of soluble metals among the solid residues investigated. The concentrations in leachates are generally low in filter cake. Moreover, it has been proven that the AOX levels are higher in the bottom ash than in both the fly ash and filter cake.