A height-adjustable implant for insertion between vertebrae, includes first and second sleeve parts which are rotationally fixed in coaxial alignment and interconnected in an axially displaceable manner. The first sleeve part has an internal thread. A nut is positioned coaxially in an inner space surrounded by the sleeve parts and is fixed to the second sleeve part so that it can rotate but is axially fixed. The nut has an external thread which engages in the internal thread of the first sleeve part. A toothed ring extends coaxially with the central longitudinal axis of the sleeve parts and is located on the nut. The second sleeve part has a radial access opening in the vicinity of the toothed ring. An operating instrument for activating the implant adjustment includes a handgrip and a shaft extending through the handgrip, a rotary grip carried on one end and another end carrying a toothed wheel for rotational actuation of the nut in the interior space of the implant.
