The accuracy of panoramic radiography (RX) and ultrasound (US) in the evaluation of both the length of the osteotomic gap and the quality of new bone formation in patients undergoing mandibular distraction osteogenesis (DO) was assessed, verifying the results against intraoperative and histologic findings. In 31 patients, three RX and three US examinations were performed after DO. RX and US findings were each independently compared, at the time of distractor removal, to the direct intraoperative measurement of the osteotomic gap and to the histologic evaluation of the maturity of a resected specimen. No significant differences (P > 0.1) resulted at any step between RX (average length: 18.19 mm) and US (18.29 mm) measurement of the osteotomic gap. In the assessment of the callus maturity the difference between RX and US (P