The incidence of skier's thumb (rupture of the ulnar collateral ligament of the first metacarpophalangeal joint) is increasing. To determine whether conservative or surgical treatment is indicated, ultrasound (US) and magnetic resonance imaging (MRI) have been advocated in the last few years. Surgery should be performed in the case of an unstable joint with a ligamentous tear or in the presence of a displaced bony fragment. Several techniques for surgical repair in acute and old ruptures are proposed. Conservative and postoperative treatment consists of immobilization of the joint in a splint or thumb spica cast for 4 weeks. The best results are obtained in bony avulsion fractures. Conservative treatment of lesions requiring surgical treatment may result in permanent disability of the joint; thus, correct diagnosis is mandatory.