Growth acceleration following femoral shaft fracture occasionally results in a significant leg-length inequality with limp. The ability to predict subsequent overgrowth would enable the surgeon to compensate for growth acceleration by providing the appropriate overriding of the fragments before the time union. The purpose of this study was to establish principles which would aid in predicting over growth. Between 1972 May and 1983 September, 115 inward patients who were 16 years old or the younger were treated in the Department of Orthopaedic Surgery of Hanyang University Hospital. In these cases, we analysed the causes of fractures, associated injury and methods of treatment. And also, by use of mentgenogram, evaluated on site, shape and degree of overriding of fractures. And then, the degree of overgrowth of bone was compared with unaffected site and analized by Bell Tompson's split orthoroentgenogram. 1. The average tibial overgrowth after fracture of femoral shaft is 2.2 mm in length. 2. The average femoral overgrowth after fracture of femoral shaft is 9.4 mm in length.