The present invention relates to a production process for 2-acrylamido-2-methylpropane sulfonic acid including at least the following successive steps: 1) mixing of acrylonitrile with at least one compound contributing SO3 at a temperature included between −80 and 30° C.; 2) placing in contact and mixing isobutylene and the sulfonating mixture with a molar ratio of SO3 to isobutylene included between 0.2:1 and 2:1 and a molar ratio of acrylonitrile to isobutylene included between 3:1 and 60:1 at a temperature included between −40 and 100° C.; 3) solid/liquid separation of the reaction mixture and isolation of the solid particles in the form of a composition 1; 4) mixing composition 1 at the end of step 3) with an aqueous solution A included at a temperature comprised between −20 and 70° C. in order to obtain a suspension 1 of 2-acrylamido-2-methylpropane sulfonic acid crystals; 5) solid/liquid separation of the suspension 1 and isolation of the crystals in form of composition 2.