Traditionally, the treatment of choice in managing pediatric femur fractures has been traction and casting. Newer methods have focused on earlier mobility and shorter hospitalization. Use of retrograde titanium elastic nails (TENs) can quicken stabilization while allowing enough motion at the fracture site to generate excellent callus. Since TENs were first introduced in North America, our Level 1 Pediatric Trauma Center has prospectively followed all of its TEN patients. In this article, we present lessons from the learning curve of our first 50 cases--focusing on complications and their prevention. In the course of obtaining predominately excellent results, we have learned several important principles regarding TEN preoperative planning, operative technique, and aftercare. The most common problem encountered has been irritation at the nail insertion site (18% of cases). Very proximal fractures may be more challenging; unstable fractures and fractures in larger, older children are best managed with a short period of adjunctive immobilization.