1. Lateral instability of the ankle may be the source of serious disability.
2. The various causes of the lesion are discussed.
3. Attention is called to the pathognomonic feature of the lesion—abnormal tilting of the talus in the joint mortise when the foot is plantar flexed and inverted at the subtalar joint. This is demonstrated in an anteroposterior roentgenogram.
4. The author describes a modifications of the classic Watson-Jones operations of tenodesis combined with reconstruction of the external lateral ligament. This method, which is simpler of execution, has the added advantage of providing greater protection against inversion of the foot by a firm sheet of fascia and retinaculum turned down as a flap and anchored over the newly constructed ligament.
5. Seven patients with chronic instability of the ankle have been treated by the author's method with good results.