Vibration damper comprising a piston rod, which is guided with freedom of axial movement in a damping medium-filled cylinder and which carries a piston, which divides the cylinder into two working spaces. At least one of the two working spaces has a flow connection leading to a housing, in which a separating element separates at least one chamber from one of the two working spaces, where the volume of the minimum of one chamber in the housing has a size which is variable within defined limits. The separating element executes relative motion with respect to the housing, and is located in a permanent position with respect to the piston rod, whereas the housing is movable with respect to the piston rod.