BACKGROUND: We investigated the use of expandable intramedullary nails, their efficacy, and short term results in the treatment of lower extremity shaft fractures. METHODS: The study included 23 patients (10 females, 13 males; mean age 33 years; range 17 to 60 years) who were treated with expandable intramedullary nails (the Fixion nail) for the lower extremity shaft fractures. Fourteen patients had femoral, nine patients had tibial fractures, all of which were closed. Eight patients had associated injuries. The mean duration from injury to surgery was 3.2 days (range 24 hours to 14 days). The results were evaluated using the Kalström-Olerud criteria. The mean follow-up was 15.3 months (range 10 to 20 months) for tibial fractures, and 13.1 months (range 10 to 19 months) for femoral fractures. RESULTS: Union was achieved in all the patients. In tibial fractures, the mean operation time was 50 minutes (range 25 to 90 min) and the mean time to union was 12 weeks (range 8 to 24 weeks). The results were excellent in six patients, and good in three patients. In femoral fractures, the mean operation time was 83.5 minutes (range 55 to 120 min) and the mean time to union was 13.2 weeks (range 10 to 20 weeks). The results were excellent in eight patients, good in three patients, fair in two patients, and poor in one patient. No complications were seen such as delayed union, early or late infections, compartment syndrome, or bone necrosis. CONCLUSION: Expandable intramedullary nails offer advantages in terms of ease of application and are less invasive than static nails and reamed applications. However, they may not provide adequate stability in metadiaphyseal regions and in fractures with fragments larger than 50 percent.