Abstract: Needle or catheter for thermally coagulating blood vessels, which mainly consists of an elongated body (2) with a proximal end (3) and a distal end (4), whereby a tip (6) in a conductive material is provided at the distal end (4), whereby a first conductor (7) which makes contact with the tip (6) extends between the distal end (4) and the proximal end (3), and whereby the outside of the elongated body (2) is provided over at least part of its length, but not at the tip (6), with an insulation (10), characterized in that the needle or the catheter (1) comprises a second conductor (8) which extends, isolated from the first conductor (7), as of the distal end (4) up to the proximal end (3) and which makes contact with the tip (6).