We analyzed the failure of Schanz pins in 234 patients with fractures of the lower extremity. All patients had the AO external fixator and stainless steel pins (ISO 58/32-1). The mean duration of treatment was 14 weeks. During this time 88 of a total of 1147 pins became loose. The first failures occurred 2 weeks after insertion. Most pins failed after 5-6 weeks. Early loosening was not accompanied signs of local infection, while late failures regularly developed pintract infections. Pins next to the fracture gap exhibited the highest rate of loosening. Intermediate pins had the lowest one. We could not detect an effect of the configuration of the external fixation. Eighty-one percent of the failed pins were exchanged consequently. We conclude that the early occurrence of pin loosening is due to mechanical reasons. Significant factors for this complications were the location close to the fracture gap and the number of pins in that segment.