Abstract: An electrosurgical system includes an electrosurgical generator to which the active and return electrodes (18, 20) of an electrosurgical instrument (12) are connected. In use the electrodes are immersed in electrically-conductive fluid to complete a conduction path between them. The electrodes (18, 20) are located on a shaft (16) of the instrument which extends from a handle (14). The shaft is covered in a translucent flexible sheath (50) comprising a tube (60) having a large proximal opening (62) to enable insertion of the instrument within the sheath, and a narrower distal opening (64) through which the distal end of the instrument shaft projects, thereby to expose the active electrode (18) to the electrically-conductive fluid.