A method for the treatment of wastewaters including a cyanide compound and a metallic compound, wherein the wastewaters are subjected to a single oxidation step during which cyanides compounds are converted into carbon dioxide and nitrogen, this oxidation step including the mixing of wastewaters with a chlorine solution and an alkaline agent so as to obtain a mixture, the alkaline agent being added in such a quantity so as to maintain the pH of said mixture between 8.8 and 9.5 and the chlorine solution being added in such a quantity so as to maintain the oxydo-reduction potential of the mixture between 150 and 450 mV.