In a nonrandomized prospective study, 111 tibial shaft fractures (55 closed, 56 open) were treated with flexible intramedullary nails. Open injuries were nailed immediately following irrigation and debridement in the vast majority of cases. Ninety-four percent of the fractures united in an average time of 18.8 weeks. There were seven nonunions (6.3%), all of which healed following a secondary procedure. Six patients demonstrated delay in union but healed their fractures within 26 weeks (5.4%). Five patients developed angulatory malunions between 6 degrees and 10 degrees after nailing (4.5%). Three patients had rotational malalignment requiring treatment (2.7%). There were four deep wound infections, which required irrigation and debridement (3.6%). In two cases the nails were retained and in two they were replaced with an external fixator. In one patient, chronic osteomyelitis developed. Flexible medullary nailing extends the indications for intramedullary fixation of tibial shaft fractures because maintenance of length, alignment, and rotation are usually possible.