The present invention relates to aqueous polymer dispersions having a polymer content of at least 55% by weight that are suitable for pressure sensitive adhesives. The invention also relates to a process for preparing these aqueous polymer dispersions and the use of the aqueous polymer dispersions in pressure sensitive adhesives and, respectively, pressure sensitive adhesive compositions, especially in pressure sensitive adhesives for transparent substrates, such as plastics labels. The aqueous polymer dispersions have a polymer content of at least 55% by weight, based on the total weight of the dispersion. The polymer is composed of ethylenically unsaturated monomers and has a glass transition temperature below −10° C., in which the dispersed polymer particles have a polymodal particle size distribution, in which at least 70% by weight of the polymer particles have a particle diameter of below 350 nm.