Subtalar joint insufficiency syndrome (S.I.S.) is the suggested description of a subtalar joint complaint characterised by instability due to active or structural stabilisation loss or slackness due to passive stabilisation loss. Insufficiency due to instability may thus be dynamic or mechanical where dynamic insufficiency includes secondary insufficiency deriving from nervous complaints (central, peripheral or proprioccptivc) and mechanical insufficiency includes secondary insufficiency deriving from heel malformation (varus or valgus). Insufficiency due to slackness, however, should be related to traumatic, degenerative or morphogenctic ligament damage particular alfecting interosseal astragalo-calcaneal ligaments and dorsal and lateral calcaneocuboid ligaments. S.I.S. is essentially subjective. Apart from possible severe distortion and pain due to seno-tarsal syndrome during the early stages, the most important feature of the complaint is heel instability. The patient does not feel sure on his feet, particularly on uneven ground, and the foot has a tendency to give way when weight is put on it. The objective importance of heel instability affecting one foot is only significant when external tibiotarsal slackness has been excluded. The possibility of heel varus or valgus, senotarsal syndrome and widespread ligament slackness should be investigated. Neither X-ray examination nor arthrographic examination are helpful in this case. Treatment may consist of physiotherapy or surgery. Physiotherapy is advisable in cases of mild or severe loss of active stabilisation due to neurological injury (especially peripheral) or proprioceptive damage. Apart from the classic subastragalar arthrodesis, present-day surgical treatment is closely linked to current theories on foot biomechanics and anatomy. These are represented by heel direction osteotomy (subthalamic and Dwyer's), interosseal ligament reconstruction.