Seven of 59 (12%) bipolar hemiarthroplasties for displaced femoral neck fracture were classified as failures at the 3-year follow-up examination. Two prostheses dislocated, 4 had loose femoral stems, and 1 was revised to a total hip arthroplasty because of pain. No patients developed acetabular erosion or deep infection. Only four of 15 patients examined by fluoroscopy shared movement between outer metal/cartilage and inner metal/polyethylene surfaces. All movement occurred at the outer metal/cartilage surface in the remaining nine patients. We conclude that the low failure rate, which compares favorably with the best results after internal fixation, is caused by the optimal selection of patients for this operation (high age, low activity level) and the use of bone cement. The bipolar design is less important, since most of these prostheses function as ordinary unipolar prostheses after some time.