Diaryliodonium salts are useful arylating reagents that have been exploited widely. In this Communication, we demonstrate that heating diphenyliodonium triflate in the solvent DMSO leads to an unexpected arylation reaction. It is postulated that arylation of DMSO at oxygen, followed by a thia-Sommelet–Hauser rearrangement, leads to the formation of 2-thiomethylphenols. More substituted diaryliodonium salts and cyclic diaryliodonium salts are shown to be more stable and less likely to react with DMSO. In conclusion, when using iodonium salts dissolved in DMSO, beware of side-reactions.