A method of determining and/or recognising, using a data processing device, a change in position of a part (20; 100) of a body structure relative to a marker device, the method comprising the following steps: preoperative data of the body structure which comprise information about the preoperative position of the part (20; 100) of the body structure relative to the marker device, are provided; intraoperative data of the body structure which comprise information about the intraoperative position of the part (20'; 100') of the body structure relative to the marker device are provided; based on the preoperative position of the part (20; 100) and the intraoperative position of the part (20'; 100') of the body structure, it is automatically determined whether the position of the preoperative part (20; 100) differs from the position of the intraoperative part (20'; 100') and/or the preoperative position of the part (20; 100) an the intraoperative part (20'; 100') is automatically displayed such that the difference in position is recognisable; and based on the preoperative data, it is automatically determined whether the preoperative part is a sub-part of a sub-structure of the body structure which is larger than the preoperative part and comprises the latter, characterised in that a change in shape of the part is determined automatically based on the preoperative shape of the part and the intraoperative shape of the part, and that a changed shape of the substructure is determined based on the plastic or elastic properties of the substructure and/or the assumption that the volume of the area which the substructure takes up has stayed constant or has changed only to a specific extent. preoperative data of the body structure which comprise information about the preoperative position of the part (20; 100) of the body structure relative to the marker device, are provided; intraoperative data of the body structure which comprise information about the intraoperative position of the part (20'; 100') of the body structure relative to the marker device are provided; based on the preoperative position of the part (20; 100) and the intraoperative position of the part (20'; 100') of the body structure, it is automatically determined whether the position of the preoperative part (20; 100) differs from the position of the intraoperative part (20'; 100') and/or the preoperative position of the part (20; 100) an the intraoperative part (20'; 100') is automatically displayed such that the difference in position is recognisable; and based on the preoperative data, it is automatically determined whether the preoperative part is a sub-part of a sub-structure of the body structure which is larger than the preoperative part and comprises the latter, characterised in that a change in shape of the part is determined automatically based on the preoperative shape of the part and the intraoperative shape of the part, and that a changed shape of the substructure is determined based on the plastic or elastic properties of the substructure and/or the assumption that the volume of the area which the substructure takes up has stayed constant or has changed only to a specific extent.