The invention relates to an active roll stabilisation system for ships, comprising at least one rotatable stabilisation element extending below the water line, sensor means for sensing the ship's movements and delivering control signals on the basis thereof to driving means for rotating the stabilisation element for the purpose of damping the ship's movements that are being sensed. The object of the invention is to provide an active roll stabilisation system for ships that can be used both while the ship is sailing and while the ship is at anchor. According to the invention, the active roll stabilisation system is to that end characterized in that the system furthermore comprises displacement means for moving the stabilisation element with respect to the ship. This makes it possible to create a relative movement of the rotating stabilisation element with respect to the water both while the ship is sailing and while the ship is at anchor, so that the Magnus effect will occur at all times and the correction force thus being generated can be utilised for damping the ship's movements that are being sensed.