The treatment of lunotriquetral interosseous (LTIO) ligament injuries is controversial. It is part of a spectrum of injuries involving the ulnar side of the wrist. Associated injuries may play a greater role in the outcome of treatment than does the LTIO injury. Arthroscopy is the most accurate diagnostic tool available for the evaluation of LTIO ligament injuries; it allows diagnosis and often treatment of associated injuries. This article describes the current approach to the diagnosis and treatment of LTIO ligament injuries and related use of arthroscopy.