A functional electrical stimulation system (30) for controlling the movement of a portion of a body of a subject (12), such as the subject's legs. The system (30) comprises a sensor (60) that in one arrangement is mountable to a portion of the subjects' body other than the legs, for example the torso (14). In another arrangement, the sensor (60) can be mountable to a walking aid, such as a crutch (20). The sensor (60) outputs signals representative of the position and/or movement of the torso (14) or walking aid (20). The system (30) also comprises a control means (32) that receives and processes the signals output by the sensor (60) and outputs control signals to a stimulator (35) adapted to provide electrical stimulation to the legs via electrodes (53) in response to the position and/or movement of the torso (14) or walking aid (20) as determined by the sensor (60).