Patients with bony defects of the proximal femur after trochanteric fracture, implant failure (cut-out), periprosthetic fracture or aseptic loosening of prosthesis are difficult to treat with primary or revision endoprosthesis. Modular femoral hip prosthesis (MHP) with stems of different length and the possibility of distal interlocking screws are an operative solution for those patients. In a prospective study from January 1996 to January 2002 all patients treated with a MHP because of proximal and / or distal femoral bony defect or fracture were included. Follow-up after 6 to 30 months was evaluated clinically and radiologically in hospital. Change of modified Harris Hip Score and radiological signs of loosening (radiolucent line, migration of MHP, breaking interlocking screw) were documented. 106 patients with a follow-up of 58.5 % were included in the study. At time of follow-up clinical and radiological outcome after trochanteric fracture was good. Harris Hip Score was comparable to the situation of patients before fracture, only one MHP was loose. However in patients after revision arthroplasty 25 % of MHP were loose and in many patients the interlocking screw was broken. Distal interlocking screw in MHP prevents stability after trochanteric fracture to achieve osseointegration. However in case of periprosthetic fracture or revision arthroplasty MHP shows insufficient stability in many cases.