A tissue access system for tissue ablation without open surgery includes a distally open elongated tube (4) with a handle piece (6) having a through channel (7) in axial alignment with the elongated tube and an infusion fitting (9) that opens into the through channel for supplying a liquid or gaseous medium. An energy guide (16) or a catheter (10) housing such energy guide is arranged in the elongated tube and sealed from the outside. An energy-releasing zone of the energy guide is located in an energy-transparent section of the elongated tube. The medium, introduced into an annular flow channel between the energy guide or catheter and the elongated tube, serves as coolant for the energy-releasing zone and as heat transport medium in the tissue, and can also function as an ablation agent and as a contrast agent for inspection using imaging techniques.