To assess the effectiveness of different surgical options in the treatment of nonunion of a femoral shaft fracture after initial intramedullary nailing. Retrospective. University hospital. During a seven-year period a total of 278 skeletally mature patients with 280 fresh femoral shaft fractures were treated by intramedullary nailing. Of these patients, a subgroup of consecutive patients with nonunion of the fracture were subjected to a detailed analysis and were followed until the fracture was united (mean thirty-three months). Injury mechanism, fracture pattern using various established classifications, any possible concomitant injuries, complications, and subsequent surgical interventions were recorded. Of the total of 280 fractures, nonunion was observed in thirty-four patients with thirty-five fractures (12.5 percent). To achieve solid union, one reoperation was sufficient in twenty-five fractures, six fractures had to be operated on twice, and four needed three operations. There were five patients with autogenous bone grafting alone, and all five required a further reoperation for the nonunion. After a dynamization procedure, four of seventeen patients required a further reoperation. After eight exchange nailing procedures, further surgery for nonunion was necessary in only one case. Solid union was achieved within six months after the final successful reoperation. A marked shortening of the femur developed as a local complication in six cases, four of which had undergone dynamization as final treatment before solid union. Exchange nailing without extracortical bone grafting seems to be the most effective method to treat a disturbed union of a femoral shaft fracture after intramedullary nailing. Autogenous extracortical bone grafting alone proved to be insufficient. Dynamization predisposed to shortening of the bone.