1. The findings in this series of fractures of the shaft of the femur treated by intramedullary nailing confirm the observation of Smith (1959) that the incidence of non-union is significantly diminished when operative intervention is postponed more than one week from the time of the injury.

2. The series is too small to afford conclusive proof, and it offers no explanation of the opposite findings of Smith and Sage (1957), but it indicates that this very important aspect of the operative treatment of fractures ought to be submitted to thorough investigation by many more observers.