Subtalar joint insufficiency syndrome (S.I.S.) is the suggested description of a subtalar joint complaint due to active instability or passive slackness, or structural stabilization lass. Insufficiency due to instability includes secondary insufficiency deriving from nervous complaints (central, peripheral or propriocettive); insufficiency due to slackness should be related to traumatic, degenerative or morphogenetic ligament damage particular affecting interosseal astragalo-calcaneal ligament; structural insufficiency includes secondary insufficiency deriving from heel malformation (varus or valgus). S.I.S. is essentially subjective. Apart from possible severe previous distortion and pain due seno-tarsal syndrome during the earlv stages, the most important feature of the complaint is heel instability. The patient does not feel sure on is foot, particularly on onefooted standing, and has tendency to give on two footed standing. The objective importance of heel instability affecting one foot is only significant when external tibio-tarsal slackness has been excluded The possibility of heel varus or valgus, seno-tarsal 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 loss of active stabilisation due to neurological injury (especially peripheral) or proprioceptive damage. Apart from the classic subtalar arthrodesis, present-day surgical treatment is closely linked to current theories on foot biomechanics and anatomy: this is, especially, represented by heel direction osteotomy (subtalamic and Dwyer's), interosseal ligament reconstruction.