SummarySkier’s thumb is an injury to the ulnar collateral ligament (UCL) of the thumb metacarpophalangeal joint (MCPJ) which has a serious risk of disabling chronic instability if not treated adequately. The lesion most often occurs in skiers when the ski pole forces the thumb to deviate radially. Strapless poles do not decrease the incidence of skier’s thumb, but if skiers are trained to discard the pole during a fall the risk might be reduced. Clinical and anatomical findings and the understanding of the injury mechanism show that stability testing (performed with the joint in full flexion) and additional standard radiographs remain the keystones in decision making in all MCPJ sprains. Protective splinting is advocated in stable, undisplaced avulsion fractures and incomplete ligamentous lesions of the UCL. However, surgery should not be delayed where there are displaced bony avulsion fractures, and where a complete ligamentous rupture is suspected because of a more than 30° stressed radial deviation and more than 20° difference compared with the uninjured side. Controlled active range of motion exercises can usually be started 3 to 4 weeks after the injury or open surgical repair, respectively. Protective splinting is continued until the sixth week and unrestricted use allowed 12 weeks following injury.