Background Studies have shown that the degree of initial displacement and also comminution of the femoral calcar, size of the head and varus angulation are prognostic of failure in displaced femoral neck fracture. We have applied these radiographic criteria in order to select patients who would benefit from internal fixation as opposed to primary hemiarthroplasty, and this prospective study was conducted in order to monitor the results of this strategy.Methods 683 displaced fractures of the femoral neck were treated with internal fixation or primary hemiarthroplasty based on the proposed radiographic criteria in a prospective consecutive study, and the patients were followed for 1-6 years. We treated 228 fractures with internal fixation and 455 by bipolar hemiprosthesis. The choice of operation was based on clinical evaluation of the patient and assessment of the assumed healing potential of the fracture, as determined by radiographic evaluation. Revision and mortality were primary endpoints.Results 54 (24%) of the patients originally treated by osteosynthesis were revised, whereas 9 (2%) of the patients treated with hemiarthroplasty had revision surgery. There were no significant differences in mortality between the groups at 30, 120 or 365 days.Interpretation Even when treating only the fractures with the assumed best healing potential with internal fixation, the results are inferior to hemiarthroplasty.