The invention relates to a new process for the production and/or purification of the salt of the compound (S)-2-[4-(2-fluorobenzyloxy) benzylamino]propanamide, i.e. ralfinamide, or the respective R-enantiomer, with methane sulfonic acid in high yields and very high enantiomeric and chemical purity in the form of the crystalline anhydrous polymorph identified as form A, wherein said salt is substantially free from impurities having genotoxic effect, such as (C1-C5)alkanylmethanesulfonates, and residual solvents known as potential precursors thereof, such as (C1-C5)alkanols or esters thereof with lower alkanoic acids.