Purpose: The aim of this prospective clinical study was to compare the clinical and radiographic results of 3 modes of implant treatment in combination with an overdenture in patients with extremely resorbed mandibles. The 3 treatment strategies used were a transmandibular implant, augmentation of the mandible with an autologous bone graft followed by placement of 4 endosseous implants, and the placement of 4 endosseous implants only. Materials and Methods: Sixty edentulous patients met the inclusion criteria and were assigned according to a balanced allocation method to 1 of the 3 groups. Postoperative complications, implant survival, periodontal indices, change in mandibular bone height, and prosthetic complications were assessed during a 2-year evaluation period. Results: During the evaluation period significantly more implants were lost in the transmandibular implant and the augmentation groups compared to the group with endosseous implants only. Except for the Bleeding Index and the Periotest values, the periodontal parameters did not differ significantly among the groups. In all 3 groups, there was no significant bone loss at most locations. Minimal prosthetic retreatment was necessary. Discussion: Although implant loss is a frequently used outcome measure for success, the necessity of retreatment seems to be of more relevance for both the patient and the clinician. Conclusions: The results of this study suggested that patients with extremely resorbed mandibles can be treated with implants alone in this patient population. (More than 50 references.)