The invention relates to a method for producing hydroxycarboxylic acids, preferably a- and ß- hydroxycarboxylic acids, from ammonium carboxylates of general formula (I), wherein R1, R2 and R3 are independently H, OH, (C1-C6)-alkyl optionally substituted with a hydroxyl group, (C1-C6)-alkenyl optionally substituted with a hydroxyl group, (C1-C6)-alkoxy optionally substituted with a hydroxyl group, (C1-C6)-alkylthio-(C1-C6)-alkyl optionally substituted with a hydroxyl group, (C6-C10)-aryl optionally substituted with a hydroxyl group, (C7-C12)-aralkyl optionally substituted with a hydroxyl group, (C3-C5)-heteroaryl optionally substituted with a hydroxyl group, on the proviso that at least one hydroxyl group is contained in at least one radical R1, R2 and R3, preferably R1 = H, CH3, CH2CH3, C6H5, (CH2)2SCH3 and R2 = H, CH3 and R3 = OH, equally preferably R1 = CH2OH, CHOHCH3 and R2 = R3 = H, CH3, especially preferably R1 = R2 = CH3 and R3 = OH, equally especially preferably R1 = CH2OH, R2 = CH3 and R3 = H. Said method comprises the following steps: an aqueous starting solution containing the ammonium carboxylate is heated, the hydroxycarboxylic acid and ammonia being formed by thermal decomposition of the ammonium carboxylate and at least part of the free water and the formed ammonia being removed from the solution at the same time, thereby obtaining a product fraction containing the hydroxy carboxylic acid. Said method is characterised in that the content of the ammonium salt in the starting solution is less than 60 wt. %, and the thermal decomposition of the ammonium salt and the removal of the free water and formed ammonia are carried out in a method step, the turnover of the ammonium salt being more than 20 mol%, preferably more than 30 mol%, preferably more than 50 mol%, especially preferably more than 75 mol%, specifically preferably more than 90 mol%, and especially more than 95 mol%, and neither ether, alcohol or hydrocarbon is used as an entrainer.