A connecting element for a spinal column stabilization system includes a first attachment section for fixing to a first bone attachment device, a second attachment section for fixing to a second bone attachment device and an at least partially flexible intermediate section. The intermediate section is arranged between the first and the second attachment section and is in the form of a strip-like, winding leaf spring element having at least one recess. A desired spring stiffness is maintained as precisely as possible, especially in the intermediate section independently of possible manufacturing tolerances arising from the manufacturing process. At least one of the two leaf spring element surfaces of the leaf spring element includes at least one stiffness-modifying element. The connecting element may be part of an improved spinal column fixation system and made by an improved method of manufacturing a connecting element.