The title compound, (C5H11OS)[RhCl4(C2H6OS)(2)], is built up of [(CH3)(2)SCH2C(O)CH3](+) cations and [RhCl4 {(CH3)(2)SO)(2)](-) anions held together by van der Waals forces. The sulfonium cation is derived from an unprecedented deoxygenation reaction of dimethyl sulfoxide. The Rh-III atom has a nearly octahedral environment, including two trans S-bonded sulfoxide ligands (dmso-S).