New trifluoromethyl-substituted imidazo[4,5-b][1,4]oxazines were synthesized by the condensation of 4,5-dihydroxy-4,5-bis(trifluoromethyl)imidazolidin-2-one with 2-aminoethanol and 2-aminophenol. An un­usual pathway was observed in the reactions of 1-methyl- and 1-phenyl-4,5-dihydroxy-4,5-bis(trifluoromethyl)­imidazolidin-2-ones with 2-aminoethanol, which led to the formation of 5-[(2-hydroxyethyl)amino]-3-methyl(phenyl)hydantoins. 1-Methyl- and 1-phenyl-4,5-dihydroxy-4,5-bis(trifluoromethyl)imidazolidin-2-ones reacted with 2-aminophenol under similar conditions to give rearrangement products, 5,5-bis(trifluoromethyl)­hydantoins. The molecular structure of 5-[(2-hydroxyethyl)amino]-3-methyl-5-(trifluoromethyl)imidazolidine-2,4-dione was determined by X-ray analysis.