Process for preparing 1,3-disubstituted imidazolium salts of the formula I where R1 and R3 are each, independently of one another, an organic radical having from 1 to 20 carbon atoms, R2, R4 and R5 are each, independently of one another, an H atom or an organic radical having from 1 to 20 carbon atoms, X is the anion of a hydrogen acid having a pKa of at least 2 (measured at 25° C., 1 bar in water or dimethyl sulfoxide) and n is 1, 2 or 3, wherein a) an α-dicarbonyl compound, an aldehyde, an amine and the hydrogen acid of the anion X− are reacted with one another and b) the reaction is carried out in water, a solvent which is miscible with water or a mixture thereof.