A retrospective study was done of 22 patients with complex femoral (11) and tibial (11) shaft fractures treated with static interlocking nailing followed by dynamization, which was carried out on average 7.8 months later. The success rate was 54% with no significant difference between the healing of femoral and tibial fractures. The follow-up was at least 2 years. The interval from nailing to dynamization did not correlate with the success rate; the longest interval associated with successful healing was 20 months. The authors found that static interlocking nailing without dynamization can still produce a high union rate, and if there is sparse callus formation during the healing process, indicating low osteogenesis, dynamization will result in fracture union in only half the cases. To improve the union rate, cancellous bone grafting may be necessary.