Apparent superomedial migration of the femoral head producing the 'tilt deformity' is the most frequent pattern of femoral head deformity in osteoarthritis of the hip. Previous reports have suggested a relationship to minor degrees of epiphysiolysis in the adolescent. Radiological and pathological examination of femoral heads obtained at the time of total hip replacement for osteoarthritis demonstrate characteristic abnormalities accompanying the 'tilt deformity'. It would appear that, in most patients, this pattern of femoral head migration results not from epiphysiolysis but from a remodelling process in the osteoarthritic joint.