A surgical instrument comprises a hollow tube (18) having a cutting window (16) at the distal end portion. An inner tube (15) is disposed within the tube (18) and is mounted for rotation about its longitudinal axis. A cutting tool (17) is located at the distal end of the tube (15), and is positioned adjacent to the cutting window (16). An outer tube (14) is provided over the tube (18). A motor (5) is provided for rotating the inner tube (15), and saline is fed to the cutting window (16) via a passageway (25) between the tubes (15) and (18). The inner tube (15) has a central lumen (24) through which tissue cut by the cutting tool (17) is removed under the action of a source of suction (12). The outer surface of the tube 18 is covered with an electrically insulating layer (22) and coagulating RF signals are supplied between the tube (18) and the outer tube (14) so as to coagulate tissue at the cutting window (16). Additional apertures (40, 42; 43, 45) in the outer tube (14) and the insulating layer (22) are aligned such that a portion of the hollow tube (18) is exposed other than in the area of the cutting window (16).