Formerly referred to as avascular necrosis, the term osteonecrosis is now preferred. Simply defined, osteonecrosis means ‘dead bone’. The ‘avascular’ state of the necrotic bone is the result of a loss of circulation from numerous potential causes together with multiple risk factors. The resultant state is a sequelae of repair processes leading finally to gross deformation of the bony structural architecture and joint incongruity. Among the commonest sites are the femoral head, talus, lunate, knee and humeral head. In addition to normal radiography, bone scan and MRI have provided early diagnosis of subtle changes in the osteo-histology. Intervention depends upon the phase of disease progression; in the form of a series of preservation and/or salvage procedures.