After the stabilization using unreamed intramedullary interlocking nails for the management of fractures of the tibial shaft, a large percentage of patients whose fractures would proceed to delayed bony union may be subject to secondary surgical procedure. The purpose of this study is to determine whether ultrasound, through its potential early assessment of the presence or absence of callus at the fracture site, can be used to predict the need for secondary surgical procedure. Fourteen tibial fractures (5 open, 9 closed) were treated with unreamed interlocking intramedullary nailing. Radiographs were obtained to monitor the maintenance of reduction and fracture healing. The results of ultrasound studies were obtained at two-week intervals for 10 weeks postoperatively and read by a radiologist. In prospective study of 14 patients, tibial fractures treated with unreamed interlocking intramedullary nailing were analyzed from June 1995 to February 1997 and following results were obtained. 1. Ultrasound correctly predicted fracture healing in all 10 fractures that subsequently progressed to fracture union. 2. Of the 4 fractures that did not heal, ultrasound was able to predict delayed union before it was radiographically evident. 3. Ultrasound predicted fracture healing at an average of 42 days (range, 22-70 days). In comparison, the plain radiographs showed fracture healing at an average of 126 days (range, 70 - 180 days). In conclusion, the tibia was ideal for ultrasound study because of the thin overlying soft tissue. Furthermore, the presence of the intramedullary nail facilitated evaluation of the intervening tissue. And there were several advantages of ultrasound over other imaging modalities. It was noninvasive, easy to use, and painless method of evaluation that does not use ionizing radiation.