Aim: Mandibular distraction osteogenesis has been used to correct the skeletal problems in patients with severe mandibular deficiency. Short-term effects of mandibular distraction osteogenesis on condylar position, condylar morphology, and temporomandibular joint symptoms in patients with severe skeletal Class II malocclusions were evaluated. Material and Methods: The records of 13 patients who had undergone bilateral mandibular lengthening and/or midline mandibular widening were analyzed. Pre- and postoperative positional changes of the mandibular condyle in the glenoid fossa, the axial rotation of the condylar head, and the temporomandibular joint symptoms were evaluated. Results: Most of the condyles were displaced in an upward and backward direction in the glenoid fossa; the amount correlated with the amount of mandibular lengthening. Resorption was observed in 20% of condyles; the incidence of the resorption correlated with incidence of preoperative articular disc displacement and with the amount of condylar displacement. Conclusion: Distraction protocols should be performed with particular attention when patients with articular disc displacement require a large amount of distraction. World J Orthod 2004;5:32–39.