This study was designed to verify whether open tibial fractures treated with an unreamed tibial nail would heal without the placement of a bone graft. Twenty-nine consecutive patients treated with unreamed tibial nails were prospectively followed to study fracture healing patterns. Monthly radiographs were studied for signs of healing without additional surgical intervention until it appeared that the fracture was a delayed union or nonunion. The average patient age was 31 years (range 16-80). Twenty-seven of the fractures were open (16 grade I, 8 grade II, 3 grade IIIA, with two additional fractures with compartment syndrome open by surgical intent. All fractures resulted from high-energy trauma. Twenty-two fractures were comminuted or segmental. Fifteen fractures healed without secondary intervention at an average of 148 days (range 98-243). Fourteen fractures needed additional intervention from between 3 and 7 months postinjury, with an average intervention of 1.9 per fracture. The two groups (primary healing and delayed union) were similar in fracture location, mechanism, and grade of injury. However, 13 of 14 delayed unions had comminuted or segmental fractures and required statically locked nails in 13 of the 14 fractures. Our experience suggests that the union rate is not improved with unreamed nails over that in the historical external fixator literature unless secondary surgical procedures are performed to change the local biology and enhance healing. We suggest early nail dynamization and bone grafting at 6 weeks to enhance and shorten healing time.