Better knowledge of pathomechanics and clinical features together with more widespread use of stressing the knee under anaesthesia and arthroscopy makes easier the diagnosis of acute knee ligament and associated injury. Careful analysis of the symptoms of chronic instability points to the hitherto neglected anterior cruciate ligament rupture as a significant knee ligament injury often causing giving-way of the knee. Prompt treatment of knee ligament rupture may offer the only hope against the irreversible injury to other knee structures caused by continuing instability.