Aqueous dispersions of water-soluble and/or water-swellable anionic polymers which are obtainable by free radical polymerization of ethylenically unsaturated, anionic monomers in an aqueous medium in the presence of at leas one stabilizer, the polymerization being carried out in the presence of at least one water-soluble polymer of the groups consisting of (a) graft polymers of vinyl acetate and/or vinyl propionate on (i) polyethylene glycols or (ii) polyethylene glycols or polypropylene glycols blocked at one or both terminal groups with alkyd carboxyl or amino groups, polyalkylene glycols, polyalkylene glycols blocked at one or both terminal groups with alkyl carboxy or amino groups and (b) water-soluble copolymers of (b1) nonionic monoethylenically unsaturated monomers, (b2) cationic monoethylenically unsaturated monomers and if appropriate (b3) anionic monoethylenically unsaturated monomers, the fraction of the interpolymerized cationic monomers being greater than that of the anionic monomers, as a stabilizer, said aqueous dispersions are prepared by free radical polymerization of the anionic monomers in an aqueous medium in the presence of the abovementioned water-soluble polymers (a) and (b) and said aqueous dispersions are used as thickeners for aqueous systems.