A process for preparing an aqueous polymer dispersion by free-radically initiated polymerization of free-radically polymerizable compounds I with moderate solubility in water, whose disperse polymer particles contain not only compounds I but also compounds II with a very low solubility in water where a mixture consisting of a portion of the compounds I and consisting of the compounds II is used to produce an aqueous emulsion I with a droplet size .ltoreq.500 nm, and at least a portion of the aqueous emulsion I is supplied continuously to the polymerization vessel as a feed stream I, in the course of continuing free-radical polymerization, during which the continuous feed stream I is accompanied, at least some of the time, by a feed stream II consisting of another portion of the compounds I or of the aqueous emulsion II thereof with a droplet size .gtoreq.1000 nm.