The principles in treatment of femoral neck fractures by primary internal fixation have been reviewed. In the rare, undisplaced stress or fatigue fracture, early internal fixation with threaded pins is recommended. Impacted fractures should be treated by primary internal fixation in patients who do not follow orders and patients whose general condition is poor and would require early weight bearing. Displaced fractures may be treated by primary internal fixation at any age and regardless of the patient's general condition. The following principles are emphasized: early operation, anatomical reduction and slight valgus in some cases, compression and impaction of fragments, and firm immobilization of fragments with a device that has a sliding mechanism and provides lateral cortical fixation.