Extensor tendon injuries of the thumb include lesions of the tendons of the extensor pollicis longus, extensor pollicis brevis and abductor pollicis longus muscles. The latter is practically only affected in open injuries. Open injuries require a tendon reconstruction by suture followed by immobilization in the distal and an adequate aftercare depending on the zone of injury. In distal injuries static splinting is applied, whereas proximal injuries from T4 on require a dynamic after-treatment. Different courses of the tendon of the extensor pollicis brevis muscle exist distal to the metacarpophalangeal joint and must be considered. The rare ruptures of the extensor hood at the metacarpophalangeal joint provoke an ulnar displacement of the extensor pollicis longus or both extensor tendons with concomitant lack of active extension in the metacarpophalangeal and interphalangeal joints. This injury is often misdiagnosed as a rupture of the ulnar collateral ligament of the metacarpophalangeal joint. It should be treated by refixation of the ruptured structures. Closed chronic ruptures of the extensor pollicis longus tendon go along with a defect that requires a tendon transfer or a tendon autograft.