Density functional theory and semiempirical methods were employed to characterize the structure and properties of sulfur-oxygen-bonded radical cations formed during the one-electron oxidation of various organic sulfides and methionine-containing peptides. In general, all of the examined sulfur-oxygen bonds can be described as two-center, three-electron-bonded systems. The usefulness of approximate computational approaches (SCC-DFTB, AM1 and PM3) for the reliable description of three-electron-bonded species was examined.