An agricultural vehicle having a hydraulic system, a cab for the vehicle operator includes a self-levelling cab suspension system having a plurality of suspension units each having a spring, a damper and an accumulator. The accumulator comprises a hydraulic working chamber which is separated by a movable wall from a gas filled chamber serving as a spring. The working chamber is also connected to a working chamber of the damper in a closed hydraulic circuit. In the invention, there is no need for a dedicated oil pump since a hydraulic actuator powered by the vehicle hydraulic system is provided for causing hydraulic fluid to flow in the closed hydraulic circuit between the working chamber of the accumulator and the damper, to vary the height of the cab without fluid from the vehicle hydraulic system entering or leaving the closed hydraulic circuit of the damper and accumulator.