The transmandibular implant system is designed for the reconstruction and rehabilitation of the edentulous mandible utilizing an extraoral approach. Transmandibular implants were placed in 19 patients and mandibular bony changes were followed using standardized panoramic radiography. Eleven sites were identified on each postoper-atiw radiograph and the percentage of radiographic enlargement was calculated for each site. The true bony changes were then computed for both short-term (9.4 months) and long-term (53.4 months) follow-up. Patients with an average mandibular height in the saddle areas of 3.5 to 8.9 mm showed bilateral bony regeneration in the saddle areas and over the most distal cortical screws of the implants. Most of these bony changes were seen in the first year, but continued beyond that time. Patients with residual bone height of 9.0 to 12.9 mm had little bone change, while patients with bone height of 13.0 to 20.5 mm demonstrated slight resorption. Theories for the observed changes are presented. The transmandibular implant is especially indicated for the severely atrophic mandible because its position within the mandible and the rigid box frame design of the implant promote bilateral bone regeneration distal to the framework of the implant. (Implant Dent 1993:2:11–17)