Seventy-nine cases of fracture of the femoral shaft treated by cast-brace and early walking have been reviewed. Discrepancy in femoral length was assessed by scanogram. The cases were analysed to relate the incidence of shortening greater than 2 centimetres to the type and site of the fracture, and the time which elapsed from injury until the cast-brace was applied. Such shortening was encountered most frequently when the cast-brace was applied within the first two weeks from injury or after six weeks and in those patients with comminuted fractures of the middle third of the femoral shaft.