A process for preparing aqueous polymer dispersions comprises first of all subjecting ethylenically unsaturated monomers to free-radical aqueous emulsion polymerization to prepare an aqueous dispersion of a polymer 1 having a glass transition temperature Tg1, then dissolving further, comparatively hard monomers in the dispersed particles of the polymer 1, and subsequently carrying out free-radical polymerization of said monomers dissolved in said particles.