Disclosed is a method for calibrating at least one 2D X-ray image of an object to be imaged, which is recorded by an X-ray device in that X-rays produced by an X-ray source radiate through the object and are recorded by an X-ray detector. An already existing 3D model of a structure of the object is compared to the 2D X-ray image, wherein an actual image positional relationship of the X-ray source and the X-ray detector relative to the object, and/or relative to one another, is determined for the 2D X-ray image.