Ruptures of the lateral ligaments of the ankle joint occur very frequently in young persons and this subject is therefore one which deserves more attention. Once a fracture or avulsion of a ligamentary insertion has been excluded the nature and extent of the ligamentary lesion should be precisely assessed. The only objective criterion of rupture of a ligament is demonstrable instability of the joint. Since the anterior talo-fibular ligament is always found to be torn immediately following supination-inversion injury to the ligaments the talar drawer sign will be demonstratable both clinically and radiologically in such cases. This test causes almost no pain and can be carried out without anesthesia. The radiological visualization of ligamentary instability with the aid of a simple jig which stresses the ankle joint provides diagnostic information which is definitely superior to that obtained from an a-p roentegenogram of the stressed joint. This conclusion was reached by statistical analysis of 384 roentgenograms.