In a method and apparatus for image support of an operative procedure implemented with a medical instrument, a two-dimensional x-ray image of a volume region to be treated is generated and stored with a C-arm x-ray apparatus in at least one pivot position of the C-arm. With a position detection device, the position of an apparatus reference system and the position of a reference system in the image generation are at least indirectly detected. Between the reference system and an image coordinate system of the x-ray image, a transformation rule is determined using known, apparatus-specific mapping rules that are measured and stored in a preceding calibration. During the subsequent procedure, with the position detection device the position of an instrument reference system is detected in the reference system and the instrument is mixed into the stored two-dimensional x-ray image with accurate position by means of this transformation rule.