In a method for geometrically correct association of at least two 3D image data of a patient, a marker field that defines a reference and is dimensionally stable and can be imaged in an x-ray image, is fixed in a stationary position relative to the patient. An x-ray apparatus is brought into first and second 3D acquisition positions. In each of the 3D acquisition positions, the x-ray apparatus acquires first 2D x-ray images for the associated 3D image data in various positions. The first and second 3D acquisition positions are selected such that a second 2D x-ray image that includes an image of at least a portion of the marker field is acquired in at least one respective position. The respective attitudes of the 3D acquisition position and the 3D image data in the reference system are determined from the image of the marker field in the second 2D x-ray image. First and second image data are geometrically correctly associated with one another according to their respective attitude.
