We performed a four-year follow-up of a randomized controlled trial involving 120 elderly patients with an acute displaced femoral neck fracture who were randomized to treatment with either a bipolar hemiarthroplasty or a total hip arthroplasty. The difference in hip function (as indicated by the Harris hip score) in favor of the total hip arthroplasty group that was previously reported at one year persisted and seemed to increase with time (mean score, 87 compared with 78 at twenty-four months [p < 0.001] and 89 compared with 75 at forty-eight months [p < 0.001]). The health-related quality of life (as indicated by the EuroQol [EQ-5D(index)] score) was better in the total hip arthroplasty group at the time of each follow-up, but the difference was significant only at forty-eight months (p < 0.039). These results confirm the better results in terms of hip function and quality of life after total hip arthroplasty as compared with hemiarthroplasty in elderly, lucid patients with a displaced fracture of the femoral neck.