OBJECTIVE: This study aimed to investigate the effect of masticatory functional changes on the lateral view morphology of the mandible in adult rats. DESIGN: Sixty 21-day-old male Sprague-Dawley rats were divided into two groups. Sixteen received ordinary (hard) food during the whole experimental period (normal group). The remaining 44 received a soft diet during 21 weeks to develop a hypofunctional masticatory system. Then, the now adult animals were divided into two equal groups: one continued on a soft diet (hypofunctional group), and the other changed to an ordinary diet with the aim of functionally rehabilitating their masticatory system (rehabilitation group). After another 6 weeks all animals were sacrificed and their left mandible was dissected, photographed and customised cephalometric software was used to perform morphometric measurements. RESULTS: The area of the mandible was smaller in the hypofunctional compared to the normal group. Interestingly, the alveolar process was shorter in the normal group. Morphometric analysis revealed significant differences such as the area of the angular process and the inclination of the condylar process. The rehabilitation group was only marginally different compared to the hypofunctional group, although a general tendency to approach (catch-up) the normal group was observed, and one morphometric variable (condylar base inclination) was indeed significantly different. CONCLUSIONS: Morphometric analysis revealed only marginal changes of the adult rat mandibular morphology during a 6-week period of masticatory function rehabilitation. However, the observed catch-up tendency might suggest that a longer rehabilitation period may have significant effect on mandibular morphology.