It was found that tetrakis(hydroxymethyl)glycoluril is unstable in aqueous solutions and undergoes stepwise dehydroxymethylation. The products of this process were identified by HPLC, 1D and 2D NMR spectroscopy. The main product of hydrolytic degradation at room temperature is tris(hydroxymethyl)glycoluril, which may be conditioned by the thermo dynamic characteristics of the reaction. Further dehydroxymethylation to give di- and monohydroxymethyl glycoluril derivatives occurs under more severe conditions.