Acetabular fracture is severe injury and is associated with other body injuries severely. It's complications are traumatic arthritis and avascular necrosis of femoral head which induce severe permanent disability and its treatment is equivocal. A clinical study was performed on 70 patients with 65 fresh fractures and 5 old fractures of the acetabulum, who were hospitalized and treated at Severance Hospital from January 1971 to December 1980 and following results were obtained. 1. The prevalent age distribution was between 20 and 50 years of age (75.7%), and the ratio between males and females was 2.2:1. The most common cause of injury was traffic accident (70.%). 2. 56 patients (80.0%) were associated injuries of other parts and the most common associated fracture was pelvic bone fracture and the most common associated soft tissue injury was urological injury. 3. A classification of acetabular fracture was induced from Judet and Letournel's anatomical classification; simple fracture was 45 cases (64.2%), associated fracture was 25 cases (35.8%) and most common hip dislocation was posterior dislocation (31.4%). 4. The methods of treatment were; closed management by using traction for 53 patients, surgical management by open reduction and internal fixation for 12 patients, and hip reconstructive surgery by total hip replacement(2 patients), cup arthroplasty (2 patients), acetabular roof formation by using iliac bone graft (1 patient). 5. The satisfactory result of conservative treatment was (57.8%), surgical treatment was (72.7%), hip reconstructive treatment was (80.0%). 6. The complications of the acetabular fracture were traumatic arthritis (36.1%), avascular necrosis (23.0%), myositis ossificans (6.6%), infection (3.3%). 7. Finally, the results of treatment depend largely on anatomical reduction, early joint motion.