Open reduction and internal fixation of the displaced fractures of the acetabulum represents one of the greatest challenge in fracture surgery. The purpose of our study is to report the results of operative treatment and establish the guideline for the operative treatment of the displaced acetabular fractures with the analysis of the clinical and radiological results. This retrospective study reports the results of 21 fractures in 21 patients(19 male and 3 female) treated by open reduction and internal fixation from January 1990 to July 1994. The patients were followed up more than 1 year and mean length of follow-up was 2.3 years. According to Letournel's classification, we had 9 elementary fractures(42.8%) and 12 associated fractures(57.2%). Among the elementary fractures, the posterior wall fracture was the most common type(7 cases, 33.3%) and the transverse-posterior wall fracture was the most common type among associated fractures(4 cases, 19.0%). Surgical approaches were 14 Kocher-Langenbeck, 6 Ilioinguinal and 1 extended iliofemoral. Indirect reduction and specially designed reduction method using C-arm and radiolucent operating table were also helpful to achieve satisfactory reduction. Overall quality of clinical results was graded according to the D'Aubigne and Postel rating score. Satisfactory reduction was gained in 16 cases(76.1%). Unsatisfactory reduction was gained in 5 cases(23.8%). Among the cases within category of satisfactory reduction, there were 7 excellent and 8 good clinical results. But among unsatisfactorily reduced 5 cases, there were 2 good clinical results. It seems that the satisfactory operative reduction of the fracture is the factor that correlates with a satisfactory clinical result. There were complications such as 3 secondary osteoarthritis(14.2%), 3 wound infection(14.2%, 2 superficial and 1 deep), 2 iatrogenic nerve palsy(9.5%, 1 sciatic and 1 obturator nerve) and 1 intrapelvic protrusion acetabuli(4.7%) and no postoperative ectopic ossification.