A balloon catheter for treating elongate diseased vessels with a variable diameter, comprising a pre-stretched balloon and a catheter shaft, which forms a wire lumen embodied to guide a guide wire and forms a liquid lumen by which a liquid can be fed to the balloon. The balloon is fastened to a first catheter shaft element at a first, proximal fastening site and fastened to a second catheter shaft element at a second, distal fastening site, wherein the second fastening site is movable along a longitudinal axis of the catheter shaft in relation to the first fastening site. The balloon surrounds a section of the catheter shaft which extends between the first and second fastening sites. Here, the section of the catheter shaft surrounded by the balloon encloses different regions of the catheter shaft with a changing longitudinal extent of the balloon.
