A simple preparation of the title compound (1) is presented. 1H N.m.r. and i.r. spectra of the fac-complex indicate only S-bonded sulphoxide ligands, confirmed by X-ray crystallographic analysis. Crystals are orthorhombic, a= 27·459(5), b= 9·925(1), c= 14·266(3)Å, Z= 8, space group Pn21a. The structure was determined by heavy-atom methods and refined by full-matrix least-squares procedures to a final R of 0·045 for 1956 reflexions. The structure consists of two crystallographicatly nonequivalent anions in the asymmetric unit linked by hydrogen bonding via dimethylammonium cations. Some mean bond distances are Ru–Cl 2·426(6), Ru–S 2·261(3), and S–O 1·48(1)Å.