The objective was to examine the effects of a lateral functional shift of the rat mandible and the effects of a shift release on the condylar cartilage during the growth period. Fifty 5-week-old male Wistar rats were initially divided into three groups: shift, recovery, and control. At 5 weeks of age, each animal in the shift and recovery groups received an appliance designed to produce a lateral functional shift of the mandible to the left side. For the recovery group, the appliance was removed after 2 weeks. For the shift group, the appliance was used for 4 weeks. Total cartilage thickness, 5-bromo-2'-deoxyuridine-labeling index, and toluidine blue and tartrate-resistant acid phosphatase-positive cell number in the condylar cartilage at 1, 2, 3, and 4 weeks were compared with those in age-matched controls that had no appliances. In the shift group at 2 weeks, the cartilage thickness and labeling index increased in the central region on the contralateral side, whereas these decreased in the lateral region on the ipsilateral side. However, in the recovery group, 1 to 2 weeks after appliance removal, the cartilage thickness and labeling index in both investigated regions became similar to the control groups. These results emphasize the importance of early treatment to normalize occlusion and create appropriate conditions for normal occlusal development.