Purpose: The objective of this clinical study was to determine the relationship of mandibular morphology with residual ridge resorption (RRR) of implant-retained overdenture (IRO) patients. Materials and Methods: RRR was quantified as change in bone volume over 1- and 2-year periods using cone beam computed tomography and a medical imaging program. Features of the mandibular morphology, namely the gonial angle, ramus length, ramus width, corpus length, and corpus height, were measured on three-dimensional models and correlated to the RRR. A total of 25 participants were treated with mandibular IROs opposing maxillary complete dentures. By the 2-year follow-up, radiographic data for 18 patients were complete for analysis. Of these 18 participants, half fall into the low gonial angle category and the other half into the high angle. Results: The extent of RRR was highly variable among participants and ranged from −2 to +2 mm in depth over the 2-year period. The mean decrease in bone volume after the first year was 3.8 ± 4.5%. This rate decreased to 3.2 ± 4.1% after the second year. RRR occurs either by translation of the entire thickness of cortical layer apically or by thinning of the outer cortical layer. RRR was significantly correlated to gonial angle (r = .471; P = .048) and predominantly occurred in the molar region in low-angle participants and more anteriorly in high-angle participants. There was no association between RRR and ramus length (r = −.341; P = .166), ramus width (r = −.183; P =.468), corpus length (r = .057; P = .821), and corpus height (r = .097; P = .702). Conclusion: Within the limitations of this study, it may be concluded that gonial angle is significantly related to RRR associated with IROs.