In a method as well as a device for planning and/or monitoring an interventional high-frequency thermoablation, 3D image data of a region (1) of interest of a body are acquired with a tomographical imaging apparatus and are presented on an image display device. In the method, a database is provided in which, for at least one interventional instrument available for high-frequency thermoablation, a volume region for at least one high-frequency power generable with the instrument is established in which a thermoablation is achieved in a tissue with the instrument at this high-frequency power. Upon marking at least one ablation position in the image representations, a 3D object representing the volume region or a volume region derived from this is then mixed in at least semi-transparently at this ablation position. The method and the associated device enable a better planning and monitoring of an interventional high-frequency thermoablation by the user.