Frequency of fracture of the acetabulum is becoming increasingly with the increase of automobile accident. If fractures are not accurately evaluated, classified and reduced anatomically, major sequelae and complications such as traumatic arthritis, joint instability and avascular necrosis of the femoral head were highly developed. The principles of treatment are to restore the fractured acetabulum to its normal anatomy, to maintain and/or restore function, and accordingly early joint motion to promote healing and to prevent joint adhesion. However, the treatment of displaced fracture of the acetabulum has been controversial: that is, should these fractures be treated by closed or open method? Judet et al(1964), Pennal(1980) and Matta et al(1986) advocated open reduction and internal fixation for displaced fractures of the acetabulum. Especially, Matta et al reported that displaced fracture must be reduced to a displacement of 3mm or less, in addition to congruent reduction of the femoral head with weight-bearing dome of the acetabulum, to achieve a satisfactory clinical result. However, some authors reported that, if closed reduction such as traction was used, good result could be obtained. We analysed 42 cases of acetabular fractures to compare the results of closed treatment with that of open treatment as well as its complication after each treatment. All were treated at Kang-Nam St. Marys Hospital from June 1981 to June l86. The complications were' developed in 7(29.2%) out of 24 cases of conservatively treated group, and 5 (27. 8 %) of 18 cases of surgically treated group. However, 7 (70%) of 10 conservatively treated cases of displaced fracture developed complication. In all conservatively treated cases, traumatic arthritis was developed. Five of 18 surgically treated patients developed complications, such as deep wound infection in two cases, traumatic arthritis in two cases, and avascular necrosis in one case. The causes of complication in 5 surgically treated cases were wrong surgical approach by wrong classification in three cases, failure of internal fixation in a case and inevitable avascular necrosis in a case, respectively. Thus, anatomical restoration of the joint surface offered the best chance for a symptom free hip and reduced the complication such as traumatic arthritis. Even though traumatic arthritis and avascular necrosis may develop later by other causes, total hip replacement surgery will be much eased, if the nor mal joint anatomy is restored at initial treatment. Proper selection of the best suited surgical approach analysing the type fracture to minimize the sequelae is mandatorily stressed when surgical treatment is indicated.