Introduction: The incidence of nonunion after fractures of the distal femur is up to 6%. The distal femoral nonunion is a disabling disease that needs complex steps in his treatment. Aim of our study is to find predicting factors of non-unions.Materials and Methods: We retrospectively analyzed 116 cases of distal femoral fractures and 20 cases of non-unions. In both surgeries we analyzed: accuracy of reduction, stability of fixation, hardware used, residual medial or lateral bone defect, use of autologous or heterologous bone grafts.Results: Malreduction, particularly axial defect, associated with unbalanced fixation, and a medial cortical bone defect of greater or lesser extent were found to be the major risk factors of nonunion. Addressing both the mechanical and the biological environment was associated with successful non union treatment.Conclusion: The main principles for solving a distal femoral nonunion are new better reduction, correction of the medial bone defect and biological support with bone grafting. From the mechanical side the association of a medial strut graft or a medial column plate could be very useful in the treatment of these non-unions. [ABSTRACT FROM AUTHOR]