In 1974, bipolar hip prosthesis was developed by Giliberty and Bateman to reduce the problems of unipolar prosthesis, including acetabular wear and acetabular protrusion, but the indications for it are still controversial. From July, 1988, to February, 1991, at Pusan maryknoll hospital, 37 hips in 33 patients of femoral neck fracture (25 hips) and avascular necrosis (12 hips) with relatively normal acetabular articular cartilage were treated with bipolar hip prosthetic replacement. The thirty-seven cases were reviewed for more than 3 years(range, 3 years to 4 years 8 months: average, 3 years 10 months), and assessed in terms of acetabular migration and function. The authors compared the datas of the femoral neck fracture with those of the avascular necrosis of femoral head. There was no statistical difference between two groups in function. But the acetabular migration of bipolar hip prosthesis used in femoral neck fracture was lesser than that of avascular necrosis of femoral head, and the serial acetabular migration disclosed gradual decrease. The authors concluded that the results of bipolar endoprosthesis used in femoral neck fracture was superior than those of avascular necrosis of femoral head with relatively normal acetabular articular cartilage.