Low-intensity pulsed ultrasound accelerates bone healing via upregulation of cartilage formation and maturation phases of endchondral bone formation. The current authors evaluated the effect of ultrasound therapy on the repair of full-thickness osteochondral defects. Bilateral, 3.2 mm diameter by 5.0 mm deep osteochondral defects were created in the patellar groove of 106 adult male New Zealand rabbits. The defects were treated with daily low-intensity pulsed ultrasound therapy on the right knee. The left knee was not treated. In Part I, the effect of ultrasound therapy was evaluated at 4, 8, 12, 24, and 52 weeks after surgery. In Part II, the effect of the length of treatment (5, 10, or 40 minutes of daily ultrasound therapy) compared with standard 20 minute therapy was evaluated. The repair cartilage was evaluated and graded on a standard scale for the gross and histologic appearance. Ultrasound treatment significantly improved the morphologic features and histologic characteristics of the repair cartilage compared with nontreated controls. Earlier, better repair with less degenerative changes at later times was observed in defects treated with ultrasound. Doubling the treatment time to 40 minutes daily significantly increased the histologic quality of the repair cartilage. In the current animal model, daily low-intensity pulsed ultrasound had a significant positive effect on the healing of osteochondral defects.