Process for preparing isophorone by 1. catalysed aldol condensations with acetone as a reactant; 2. workup of the reaction product, the workup in stage 2 being effected so as to give three fractions: a) a fraction composed of unconverted acetone, water and low boilers, which is condensed and then recycled into the reactor for reaction; b) a fraction in which colouring substances in particular are enriched, this fraction being purified further and the materials of value present being recycled into the process; c) a fraction composed of isophorone, more highly condensed products and water and catalyst, called material of value stream, this fraction subsequently being subjected to a hydrolysis 1 in which by-products are converted partly or fully to isophorone, acetone and other products of value; 3. wherein the worked-up fraction c) is subjected to a phase separation into an essentially organic fraction d) and an essentially aqueous fraction e); 4. distillative workup of the aqueous fraction e) and passage of the vapours from the top of the distillative workup apparatus onward into the hydrolysis apparatus 1; 5. purification of the organic fraction d) to give the following three fractions: i) residue, ii) pure isophorone, iii) remaining low boilers; 6. hydrolysis 2 of the residue i) and recycling of the products of value formed into the process. 1. catalysed aldol condensations with acetone as a reactant; 2. workup of the reaction product, the workup in stage 2 being effected so as to give three fractions: a) a fraction composed of unconverted acetone, water and low boilers, which is condensed and then recycled into the reactor for reaction; b) a fraction in which colouring substances in particular are enriched, this fraction being purified further and the materials of value present being recycled into the process; c) a fraction composed of isophorone, more highly condensed products and water and catalyst, called material of value stream, this fraction subsequently being subjected to a hydrolysis 1 in which by-products are converted partly or fully to isophorone, acetone and other products of value; a) a fraction composed of unconverted acetone, water and low boilers, which is condensed and then recycled into the reactor for reaction; b) a fraction in which colouring substances in particular are enriched, this fraction being purified further and the materials of value present being recycled into the process; c) a fraction composed of isophorone, more highly condensed products and water and catalyst, called material of value stream, this fraction subsequently being subjected to a hydrolysis 1 in which by-products are converted partly or fully to isophorone, acetone and other products of value; 3. wherein the worked-up fraction c) is subjected to a phase separation into an essentially organic fraction d) and an essentially aqueous fraction e); 4. distillative workup of the aqueous fraction e) and passage of the vapours from the top of the distillative workup apparatus onward into the hydrolysis apparatus 1; 5. purification of the organic fraction d) to give the following three fractions: i) residue, ii) pure isophorone, iii) remaining low boilers; i) residue, ii) pure isophorone, iii) remaining low boilers; 6. hydrolysis 2 of the residue i) and recycling of the products of value formed into the process.