In brief Injury to the ulnar collateral ligament of the thumb is relatively common among skiers. Because the injury has a propensity for causing long-term complications, patients require meticulous follow-up and-if the ligament is unstable, or if the stability of the injured ligament is unknown-early referral. X-rays are imperative for ruling out fractures, and they sometimes show the extent of injury. Stress examination will also help delineate management. Primary care physicians can treat most incomplete sprains successfully with a thumb cast followed by hand or occupational therapy; patients with complete ruptures should be referred to an orthopedist.