Between 1973 and 1982 we treated 569 fractures of the femoral shaft by means of osteosynthesis. The internal nailing was performed in 41.6%. We used an interlocking nailing in 170 cases, 116 times statically and 54 times dynamically. An open reposition was performed in 48.2%. With only a very small incision we exposed the area of the fracture to insert the reamer guide under control of the fingers into the distal part of the femoral shaft. By using this technique there is no danger of disposing the fragments in order to achieve stabilisation in the correct position. 52.4% of the patients were younger than 30 years and 25.9% older than 30 years and 25.9% older than 60 years. In all cases we observed an osseous healing, twice a secondary cancellous bone craft was necessary. As complications we had an infection rate of 2.9%, loosening of the bolt in 0.6%, axial malalignment greater than 10 degrees in 0.6%, a rotary malalignment greater than 10 degrees in 1.2%. We did not observe any refracture. Less complications can be observed in interlocking nailing in comparison with plate osteosynthesis. Technique, indication, mistakes, and dangers as well as careful timing of operation are discussed. In open fractures delayed osteosynthesis by means of interlocking nailing is to be preferred to primary plate osteosynthesis. Fractures fixed by interlocking nailing had comparatively less complications in fracture healing and especially no more shortenings and rotation deformities, but the advantage of early full weightbearing. The interlocking nail has a very important value in the management of femoral shaft fractures.