Four patients aged 11 to 14 years sustained femoral shaft fractures. The fractures proved to be irreducible by conventional closed methods. At operation; either the proximal or distal end of the fracture was found to have 'buttonholed' through the lateral intermuscular septum, preventing reduction. The case histories and clinical results are presented. To our knowledge this complication has not been described previously, and we believe that it is an indication for open reduction and internal fixation, for reasons that will be discussed. In the patients described here there was no important leg length inequality as a result of the internal fixation.