Objective:　To analyze the causes of distal femoral nonunion and delayed union and assess the outcome of the corresponding treatment, retrograde intramedullary interlocking nail (RIIN).rn　　Methods:　From June 1995 to December 1998, 15 patients (9 males and 6 females) with distal femoral nonunion and delayed union were treated with RIIN. The average age of the patients was 34.5 years (23-46 years). Bone grafting was performed in 10 patients, closed reaming was done in the other 5 patients. Correction osteotomy was performed in 2 patients, and intra-articular release of knee adhesion in 11 patients. X-ray examination and knee society clinical rating system (KSS) were used to evaluate the results.rn　　Results:　All fractures were followed up for at least 9 months with average follow-up duration of 14.5 months (9-33 months). Solid union was documented in all patients at 6.4 months on average. There were no infections or malunions in this series. Based on the final follow-up data, acceptable functional range of motion (ROM) of over 90° was achieved in most patients. The average ROM was 93.5° with significant improvement of 28° (42.7%, P＜0.05) compared with the preoperative ROM. The average knee score was 96. Excellent ROM emerged in 13 patients. The knee function score was 90.5 on average.rn　　Conclusions:　The main causes of distal femoral nonunion and delayed union are improper indications and improper use of the implants. RIIN is an effective altative for treatment of distal femoral nonunion and delayed union because it can provide a stable and reliable fixation which is beneficial for early functional exercise of knee. Bone grafting, closed reaming and intra-articular release of knee adhesion should be considered in order to enhance the bone healing and improve ROM and the knee function.