Objective: To test the hypothesis that low-intensity pulsed ultrasound (LIPUS) stimulation does not histologically affect the growth of mandibular condylar cartilage.Materials and Methods: Thirty-five 20-day-old Sprague-Dawley rats were assigned to experimental and control groups. Experimental rats were stimulated with LIPUS in the temporo mandibular joint (TMJ) region unilaterally, for 10 or 20 minutes for 20 days. After euthanasia, histological specimens were analyzed qualitatively and histomorphometrically at the anterior and posterior aspects of the mandibular condyle, including the condylar cartilage and the area and perimeter of subchondral bony trabeculae.Results: LIPUS stimulation may alter the histological arrangement of the condylar bone and cartilage, showing qualitative differences on specimens treated for 10 or 20 minutes daily compared with controls. Cartilaginous layer thickness was not affected by LIPUS stimulation to a significant level, but was modified at the relative layer thickness within the cartilage at the anterior aspect of the condyle (P < .05). At the sub chondral bone level, 20-minute stimulation significantly increases trabecular perimeter (P = .01).Conclusions: LIPUS application may affect mandibular growth pattern in rats acting at the cartilage and bone level. The effect of LIPUS on the growing condyle is expressed through a variation in trabecular shape and perimeter. A greater response is achieved when stimulated for 20 minutes instead of 10 minutes daily. (Angle Orthod. 2009;79:964-970.