Aqueous dispersions containing a polyurethane and from 5 to 60% by weight, based on the polyurethane, of an adhesion-improving polymer, the polyurethane consisting essentially of(a) organic diisocyanates,(b) dihydroxy compounds which have a molecular weight of from more than 500 to 5,000 g/mol and contain no ionic groups or groups convertible into ionic groups,(c) compounds having one or two functional groups reactive toward isocyanate and at least one ionic group or group convertible into an ionic group and(d) compounds having at last 3 isocyante groups or at least 3 functional groups reactive toward isocyanate,(e) optionally compounds which differ from (c) and have two functional groups reactive toward isocyanate and a molecular weight of from 60 to 500 g/mol, the compounds (d) being used in amounts such that the functionality F of all components is from 2.01 to 2.5, and the polyurethane or a prepolymer thereof is prepared in a water-miscible solvent boiling below 100.degree. C. and, after addition of the adhesion-improving polymer, is dispersed in water.