The olecranon is exposed to high tension and bending forces. In 2/3 multifragment fractures occur. Tension belt and plate fixation in these not only transverse but also sagital and frontal plane fractures is often not possible. As a central weight bearing device the XS 4,5mm nail is exposed to a lower bending moment and a angle stable transverse fixation with 2,4mm threaded wires every 9mm is possible. Also a soft tissue independent fracture compression with a set screw (proximal longitudinal holes) is possible. Additional frontal and sagital plane fragments can be fixed to the system with fibre wire hemicerclages. From 5.1999 to 12.2002 80 consecutive cases with XS nail osteosynthesis of a olecranon fracture were treated and 73 (91%) could be re-examined clinically and radiological 15 months after surgery. 13,7% were open fractures 67% were 3 or more part fractures. For evaluation the Murphy score was used. The mean time for surgery was 37min for two part and 56 min. for more part fractures. The Murphy score showed in 64% very good and in 29% good results. Only in 4 patients with more part fractures with additional radius head fractures and previous surgery had fair or unsatisfactory results. The XS nail is a new concept for stabilisation of all but specially of complex and very comminuted olecranon fractures with a very low complication rate and good functional results.