Acetalized azo dyes are prepared by diazotizing an amine, coupling with a hydroxyalkyl-containing coupling component and subsequently reacting with a vinyl ether in a process which comprises carrying out the coupling reaction in a two-phase reaction mixture comprising water and an aromatic hydrocarbon, subsequently separating off the aqueous phase and reacting the azo dye, which is present in the organic phase, without intermediate isolation, with a vinyl ether in the presence of a polybasic carboxylic acid as catalyst.