The invention relates to a method and a device for determining the position of a part of a medical instrument with an x-ray sensitive sensor in a plane of an x-ray image using an x-ray facility having an x-ray beam source and a device, which is assigned to the beam source and influences the x-ray radiation emitted by the x-ray beam source, wherein a spatial region, in which the medical instrument is located, is scanned with x-ray radiation and at the same time x-ray radiation is detected with the x-ray-sensitive sensor with the device for influencing the x-ray radiation rotating at constant speed, the rotation being synchronized to the receipt of signals based on x-ray radiation with the x-ray-sensitive sensor and with the position of the part of the medical instrument in the plane of an x-ray image being determined based on the x-ray radiation detected with the x-ray-sensitive sensor.