In the cation of the title solvated molecular salt, C12H14ClN4 +·C14H8F3O2S−·C2H6OS [systematic name of the cation: 2,4-diamino-5-(4-chlorophenyl)-6-ethylpyrimidin-1-ium], the dihedral angle between the planes of the pyrimidinium and 4-chlorophenyl rings is 77.2 (5)°. In the anion, the planes of the benzene rings are twisted with respect to each other by 71.5 (5)°. Disorder was modelled for the dimethyl sulfoxide solvent molecule over two set of sites in a 0.7487 (13):0.2513 (13) ratio. In the crystal, the cations are linked by inversion-generated pairs of N—H⋯N hydrogen bonds, with an R 2 2(8) graph-set motif. The cation donates two N—H⋯O hydrogen bonds to the anion, also generating an R 2 2(8) loop. These interactions, along with cation–solvent N—H⋯O hydrogen bonds, and cation–anion C—H⋯F, solvent–anion C—H⋯O and C—H⋯F interactions, result in a three-dimensional network.