The main objectives of this retrospective multicentric study were to define the predisposing factors and methods of treatment. The common predisposing factor is the femoral fragilization due to loss of "bone stock" (secondary to osteopathies or tumor, or especially prosthetic loosening). More specific factors are iatrogenic. For intraoperative fractures we found reoperation, excessive mobilisation of the femur and excessive diaphyseal reaming. For postoperative fractures we found coticotomy and screw hole distal from the tip of the stem, or a gap between another implant wich induced a gradient of elasticity. The therapeutic indications follow the Johansson classification:Type I fractures: If the stability of the prothesis is good: - with a transverse fracture line: functional treatment (off-loading for 45 to 60 days), - with a spiral fracture line: internal fixation using a rigid plate or cerclage wire. If prosthesis loose:- revision arthroplasty with a long stem prothesis is the ideal, - if the general status is too poor, orthopaedic treatment is indicated.Type II fractures: If good stability of the prothesis: internal fixation using a rigid plate. Bone grafting is not necessary. If prosthesis loose: revision arthroplasty with long stem prothesisType III fractures: Altought the ideal seems revision arthroplasty using long stem prothesis, we think that internal fixation by plate with perfect operative technique is indicated for these old and vulnerable patients. Considering the therapeutic indications we suggest a modification of the Johansson's classification:Type I fracture: - Ia: stability of the prothesis, - Ib: loosening prothesis.Type II fracture: - IIa: stability of the prothesis, - IIb: loosening prothesis.Type III fracture: - IIIa: proximal fracture, - IIIb : distal fracture.