63 acetabular posterior wall fractures were followed up for an average of 3 years and seven months after trauma. Of 24 patients with successful manual reduction of femoral head dislocation, a small fracture fragment, no sciatic nerve injury and who were not operated on, 16 had a satisfactory result. Of 39 patients who were operated on because of the large size of fragment (over 3.5cm X 1.5cm), unstable hip joint after reduction, persistent dislocation of the femoral head and presence of sciatic nerve injury without improvement within 4 weeks, 26 had a satisfactory result, but 6 had a poor result. In 32out of 39 operative patients, loose fragments of bone of cartilage and soft tissue were observed in operative field, and they were not noted in routine roentgenogram in 14 patents. So CT scan is necessary for confirmation of presence of loose fragment or soft tissue interposition in all of the posterior wall fractures with dislocation of femoral head. The prognostic factors are the time between dislocation and reduction of femoral head, degree of injury of articular cartilage, degree of anatomical reduction and secure internal fixation of fragments in operatively treated cases, and the time to commence exercise.