The present invention relates to a method for the purification of an .alpha.-hydroxy acid on an industrial scale, in which the method involves: (a) subjecting an aqueous stream containing mainly .alpha.-hydroxy (1) to an extraction step, with the formation of an aqueous place containing mainly .alpha.-hydroxy acid (2), (b) concentrating the aqueous phase containing mainly .alpha.-hydroxy acid (2) by means of evaporation of water under reduced pressure, with the formation of a concentrated .alpha.-hydroxy acid solution in water (3), and (c) subjecting the concentrated .alpha.-hydroxy acid solution (3) to a crystallization, with formation of pure .alpha.-hydroxy acid (4), where (i) the concentrated .alpha.-hydroxy acid solution (3) is directly cooled in a melting crystallization device, and/or (ii) the concentrated .alpha.-hydroxy acid solution (3) is diluted with water and crystallization is brought about in one or more cooling crystallization devices and/or evaporative crystallization devices, and/or (iii) crystallization is brought about in one or more adiabatic crystallization devices.