The Au^III atoms in the cationic pseudo-square-planar complex tetra­kis­(1-methyl-2,3-di­hydro-1H-imidazole-2-thione-κS)gold(III) trichloride sesquihydrate reside at the corners of the unit cell on an inversion center and are bound by the S atoms of four methimazole ligands in a planar arrangement, with S—Au—S bond angles of approximately 90°.