A process for preparing salts of acrylamido-2-methylpropanesulfonic acid (A) using the steps of: preparing a solution of a contaminated salt of acrylamido-2-methyl-propanesulfonic acid (A) in an anhydrous organic solvent (L) using at least one basic component (B) selected from the group of alkali metal oxides, alkaline earth metal oxides, alkali metal hydroxides, alkaline earth metal hydroxides and amines of the formula (I) NRaRbRc  (I) where the Ra, Rb and Rc radicals are each independently: hydrogen, C1-C4-alkyl, hydroxy-C1-C4-alkyl or C1-C4-alkoxy, where the molar ratio of compound (A) to the basic component (B) is 1:1 to 1:3, recovering the dissolved salt of compound (A) by crystallization or by precipitation, by altering the temperature and/or the pressure and/or the concentration of the salt in the solution. This leads to salts which are low in by-products and are particularly suitable for polymerization.