Contaminated wastewater from the preparation of isophorone, isophoronenitrile and isophoronediamine is treated by A) 1. treating the wastewater from the preparation of isophoronenitrile from the reaction of isophorone with hydrogen cyanide by alkaline hydrolysis of isophoronenitrile to isophorone, and the salts of hydrogen cyanide within a pH range of 12.0 to 13.7 and at temperatures of 60 to 200° C., and 2. processing the wastewater from A) 1. by an oxidation, or B) treating the wastewater from the preparation of isophoronenitrile from the reaction of isophorone with hydrogen cyanide by an oxidation, or C) processing the wastewater from A) 1. and the wastewater from the preparation of isophorone and/or the wastewater from the preparation of isophoronediamine by an oxidation.