The title compound, C(8)H(12)N(2)O(3)S(2), has been isolated as a by-product in the synthesis of methyl-ene blue dye. The compound crystallizes with four independent mol-ecules in the unit cell (Z'= 4). The zwitterionic form of the mol-ecule was established on the basis of the hydrogen atom located at the dimethyl-amino group. The crystal structure is dominated by inter-molecular hydrogen bonds of the N-H⋯O type formed between amino and ammonio N-H groups and O atoms from the sulfothio-ate group. There are in addition two weak inter-molecular N-H⋯N inter-actions and some non-conventional C-H⋯O hydrogen bonds.