From 9 microwave rotational spectra of 7 isotopic species of dimethyl sulfoxide the restructure of the molecule has been calculated. However, one H-atom is positioned so near a principal inertial plane that one coordinate could not be reliably determined. A special double substitution method aimed at improving this remaining coordinate was applied with limited success; r0-structure calculations were performed and discussed based on differently chosen sets of isotopic spectra. The torsional fine structure due to the internal CH3-rotation was reanalyzed with improved structural parameters.