The invention relates to a tissue marker (1, 1′) for marking a lesion (16) in the body tissue (6). The invention is characterized in that the tissue marker (1, 1′) comprises a transponder (2). The transponder (2) can be activated by electromagnetic radiation (8) in such a manner that the transponder (2) emits a localization signal (9) in the form of electromagnetic radiation by means of which the position of the tissue marker (1, 1′) in the body tissue (6) can be detected. The invention further relates to a system for determining the position of such a tissue marker (1, 1′) and to the use of an RFID tag as a tissue marker (1, 1′) for marking a lesion (16) in the body tissue. According to an advantageous embodiment of the invention, the tissue marker (1, 1′) is biodegradable.
