The present disclosure relates to an expandable reamer having a base body, a ring section, at least one cutting edge which is geometrically defined and provided on the outer surface of the ring section, an adjustment device which works on the ring section from the inside, has an adjustment screw, and serves to adjust the radial position of the at least one cutting edge, wherein the adjustment device is arranged in a cavity provided in the base body of the expandable reamer, and an adjustment body with a conical or round outer surface. The adjustment body can be displaced in the direction of the central axis of the expandable reamer and serves for the expansion of the ring section. The expandable reamer is characterized in that the adjustment body is designed as an adjustment sleeve which surrounds the adjustment screw and is mounted in a floating manner.