BACKGROUND Periprosthetic supracondylar fractures of the femur after total knee arthroplasty are not common but are usually difficult to treat due to the advanced age of patients and frequently accompanying osteoporosis. Retrograde intramedullary nailing can be effective in promoting healing of these fractures by providing sufficient stability, but the number of beneficiaries is small due to its limited applicability and the postoperative function has rarely been assessed. This study evaluated the efficacy of retrograde intramedullary nailing for the treatment of periprosthetic supracondylar fractures of the femur using the clinical outcomes. METHODS Between January 2000 and May 2006, 9 patients (10 knees) with periprosthetic supracondylar fractures of the femur underwent retrograde intramedullary nailing. An open reduction and additional fixation using a shape memory alloy ring were used in 3 of them in whom a closed reduction was not successful. The clinical and radiographic findings were reviewed retrospectively in 7 patients (8 knees), excluding 2 who were unavailable for a follow-up assessment due to death. The mean follow-up period was 39 months (range, 24 to 82 months). The union and alignment of the fracture were assessed radiographically. The postoperative function was evaluated using Sanders' criteria. RESULTS Radiographic union was obtained in all patients after an average of 13 weeks (range, 12 to 15 weeks) postoperatively. No postoperative infection, heterotopic ossification and component loosening were observed. After union, the coronal alignment averaged 0.1 degrees valgus (range, 3.6 degrees varus to 2.6 degrees valgus) and the mean sagittal alignment was 1.9 degrees of extension (range, 0.9 degrees of flexion to 6.3 degrees of extension). The mean range of motion was 103 degrees (range, 90 degrees to 120 degrees) postoperatively. At the last follow up, there were 1 excellent, 5 good and 2 fair results according to Sanders' criteria. CONCLUSIONS With retrograde intramedullary nailing, excellent fracture union and good functional recovery were obtained in patients with periprosthetic supracondylar fractures.