An electrode for vaporising tissue comprises a head (26) supported by at least one externally insulated electrically conducting stem (27). The head (26) is typically a button electrode and is provided with a conductive portion (41) in which the surface of the button electrode is electrically conductive, and an insulated portion (37) in which the surface of the button electrode is non-conductive. The head is typically mounted on the stem (27) such that it is capable of rotating about the stem such that it can change its rotational orientation depending on the direction of movement of the electrode. Typically, the head (26) is asymmetrical such that it has a greater width in one direction as compared with another direction, such as having an oval cross-section. The head (26) is rotatable about the stem (27) such that, whichever the direction of movement of the electrode, the electrode orients itself such that it presents the greater width parallel to the direction of movement of the electrode.
