Two new polymorphs of the title compound, K[PtCl(3)(C(6)H(15)O(4)PS)], already known in the monoclinic form, were obtained by crystallization from acetone-n-pentane solutions of different composition. Both polymorphs are orthorhombic in the space group P2(1)2(1)2(1), with Z' = 1 (solvent ratio 1:4) and 3 (solvent ratio 1:9). In both polymorphs, electrostatic interactions link K(+) cations and [PtCl(3)(SMP)](-) anions [SMP is diethyl (methylsulfinylmethyl)phosphonate] in infinite chains, while adjacent chains are held together by weak C-H...Cl and C-H...O hydrogen-bond interactions.