Organopolysiloxane compositions having a 25° C. viscosity of at least 500 Pa·s., are continuously prepared by mixing and kneading organopolysiloxanes and fillers in a first process stage, in a kneading cascade having at least two kneading chambers arranged in series each containing two kneading tools on parallel axes, capable of being driven in corotating or counterrotating directions, the chambers connected to one another by means of openings through which material can pass in a direction transverse to the axes of the kneading tools, the first kneading chamber having a feed opening and the last kneading chamber having a discharge opening, to give raw mixtures and kneading and degassing the raw mixtures, in a second process stage at from 100° C. to 250° C. in a continuously operated double trough kneader having a discharge screw.