BACKGROUND: Osteoradionecrosis (ORN) of the mandible is not an uncommon complication after radiotherapy for head and neck cancers. Although definitive treatment has been confirmed as radical excision of the necrotic bone with simultaneous vascularized osteocutaneous flap reconstruction, it remains a unique challenge. In this study, we compare our results of reconstruction with free iliac and fibula flaps in flap survival, bony union, and postoperative complications. PATIENTS AND METHODS: From 1986 to 2011, there were 153 mandibular ORN cases in our center that were treated with radical resection of the necrotic bone and reconstruction with either vascularized iliac (n=108) or fibula flaps (n=45). Data collected for analysis included patient demographics, flap survival rate, postoperative infection rate, nonunion/malunion rate, mean hospital stay, and antibiotics use. RESULTS: All patients healed eventually without recurrence of ORN. However, we observed difference in the complication rate between the iliac flap group and fibula flap group. In the group with iliac flap reconstruction, patients required less days of hospital stay for intravenous antibiotics treatment postoperatively. The average days required for intravenous antibiotics in the iliac flap group were 10.46 (2.28) versus 16.09 (3.88) days in the fibula group (P<0.01). In the group with fibula flap reconstruction, 9 (20.0%) patients had subsequent neck infection due to healing problem, compared to 8 (7.4%) patients in the iliac flap group (P=0.04). In the iliac flap group, the nonunion and malunion rates were 4.6% and 2.8% respectively; whereas in the fibula group, the rates were 15.5% and 6.6%, respectively (P=0.04 and 0.36, respectively). CONCLUSIONS: For ORN patients, vascularized iliac bone flap provides more reliable results compared to fibula flap. The merits of vascularized iliac flap include the following: (1) its natural curve mimics the shape of mandible and does not need osteotomy; (2) it offers more volume of bone that matches better to the native mandible to allow later osteointegration as well as faster bony union, due to the nature of being a membranous bone; and (3) it carries more abundant soft tissue to obliterate possible dead space. The only disadvantages are short pedicle and requiring special management of skin paddle, which can be overcome by training in microsurgery.