1. The invention relates to a hydraulic tensioning element for a traction mechanism drive, having a cylinder, having an axially movable piston which is guided in the cylinder, having a spring element which is arranged between the cylinder and the piston, having a pressure space which is formed in the cylinder, and having a reservoir, which is formed in the piston, for a hydraulic fluid, and having a valve which permits an exchange of the hydraulic fluid between the pressure space and the reservoir as a function of an actuating movement of the piston, wherein the cylinder (2) has a flanged portion (17) which reduces the size of its opening, and wherein the free end of the piston (4) has formed on it an annular section (16) with a diameter which is larger than the piston diameter.