A thumb orthosis, particular for correcting malpositions of the thumb in the carpometacarpal joint, includes a) a substantially dimensionally stable molded body bent in a U-shape, which is fitted on the hand between the thumb and index finger in the applied state and supports the thumb and fixes it at a distance from the index finger, wherein the molded body bent in a U-shape has a first end portion and a second end portion, and b) a strap which is fastened by one strap end to the first end portion of the molded body, wherein the second end portion of the molded body has a guiding element for guiding the strap, for example has a turning element for turning the strap back.