The crystal structure of the title compound, [Os(C(6)H(7)S)Cl(C(18)H(15)P)(2)(CO)], confirms the formulation as an osmabenzene. There is a slightly distorted octa-hedral coordination environment at the Os(II) ion, with the triphenyl-phosphane ligands mutually trans and the chloride cis to the carbon bearing the -SMe substituent. Within the metallacyclic ring, the C-C distances are appropriate for aromatic bonds and the two Os-C distances are shorter than typical Os-C single bonds. The maximum deviation from the least-squares plane through the osmabenzene ring occurs for the carbon bearing the SMe substituent [0.1037 (18) Å].