A consecutive, prospective series of ninety-seven patients who had 100 fractures of the femoral shaft that were treated with static interlocking nailing was analyzed to determine the incidence of union of the fracture without planned conversion from static to dynamic intramedullary fixation as a technique to stimulate healing of the fracture. Eighty-four patients (eighty-seven fractures) were studied through union of the fracture (average follow-up, fourteen months). Eighty-five (98 per cent) of the eighty-seven fractures healed with static interlocking fixation. Two patients needed conversion from static to dynamic interlocking fixation because of inadequate fracture-healing; both progressed to uneventful union. The time to full weight-bearing (average, eleven weeks) was individualized for each patient and depended on the cortical contact of the major fragments, the presence of bridging callus as seen on radiographs, and the extent of other injuries of the ipsilateral lower extremity. No deformation or failure of the static interlocking device developed after early walking with weight-bearing, but fatigue failure of one nail occurred in a non-ambulatory patient who had an intracranial injury. Pain related to soft-tissue irritation by the prominent heads of the interlocking screws, clinically presenting as bursitis or snapping of the iliotibial band, was severe enough in six patients to necessitate removal of either the proximal or the distal screw after union of the fracture. We concluded that static interlocking of intramedullary nails in femoral shaft fractures does not appreciably inhibit the process of healing of the fracture, and that routine conversion to dynamic intramedullary fixation, although occasionally necessary, need not be performed.