Abstract The mixture of DMSO–water was studied with Car–Parrinello simulation techniques. A threefold coordination at the DMSO oxygen, methyl group hydrogen–oxygen atom contacts, Rüssel-structures and 1-DMSO–3-H 2O clusters are observed. The H(DMSO)–O(H 2O) and the H(DMSO)–H(H 2O) radial distribution functions are almost identical. For different far water the angular distribution displays a dialectic character: close water orient with the oxygens to the methyl hydrogen far waters vice versa. The emerging picture for the dynamical behavior of the methyl groups is that of a near-hydrophilic–far-hydrophobic, where the hydrophobic character is probably dominant. A detailed mechanism of one such an event is given.