An insertion system for release of a self-expanding stent device 18 in a body vessel has a first grip 33, which is fixedly connected to a shaft 15, a second grip 36, which is mounted on the shaft 15 to be movable in axial direction, a sheath 19, which, in a distal portion thereof, keeps the stent device radially compressed and which is fixedly connected to the second grip 36, and a retention element 17, which is fixedly connected to the shaft 15 and is guided in the sheath 19, wherein the retention element 17 holds the stent device 18 in its axial position relative to the first grip 33 when the sheath 19 is being retracted. Reference means 25 with an optical reference mark 26 are arranged for continuous monitoring of the axial position of the stent device 18.
