A tear of the acetabular labrum with interposition following the reduction of posterior dislocation of the hip should be suspected when: (1) the femoral head does not clunk into the acetabulum at the time of the reduction, (2) the hip is unstable after manipulation even though there is no fracture, and (3) the roentgenograms of the pelvis show the femoral head to be resting further from the acetabulum on the affected side than on the non-affected side. The fibrocartilaginous labrum should be reattached to the acetabulum.