An electrosurgical instrument for the treatment of tissue in the presence ofan electrically-conductive fluid medium comprises an instrument shaft (10),and an electrode assembly (12) at one end of the shaft. The electrode assembly(12) comprises a tissue treatment electrode (14) and a return electrode (18)which is electrically insulated from the tissue treatment electrode by meansof an insulation member (16). The tissue treatment electrode (14) has an exposedsurface for treating tissue, and the return electrode (18) has a fluid contactsurface so as to define, in use, a conductive fluid path that completes an electricalcircuit between the tissue treatment electrode and the return electrode. Thetissue treatment electrode (14) is provided with at least one aperture (14a)through which vapour bubbles and/or particulate material can be aspirated fromthe region surrounding the tissue treatment electrode, and the tissue treatmentelectrode and the insulation member are disposed such that there is a gap therebetweenforming an additional suction channel (25).
