Distraction osteogenesis is useful in the reconstruction of mandibular segmental defects. The effects of radiotherapy on distracted bone after resection of squamous cell carcinoma of the oral cavity are still unknown. We report the outcome in six patients who had distraction osteogenesis after postoperative radiotherapy. Distraction was by a unidirectional semi-buried device and panoramic radiographs were taken monthly during the distraction and consolidation periods to monitor the progress of the distraction. Follow-up ranged from 15 to 45 months (mean 33). The dose of radiation ranged from 60 to 70Gy. In one patient the bone was completely exposed and all the screws were loosened. There was no calcification and the gap remained radiolucent in the panoramic radiographs. The other five patients had excellent or good quality of bone. We conclude that radiotherapy may not interfere substantially with distraction osteogenesis although larger series the necessary.