Purpose: This study assessed the impact of mandibular bone height on masticatory performance following treatment with a mandibular conventional denture (CD) or implant-retained overdenture (IOD). Materials and Methods: Evaluation of masticatory performance in 63 participants was made with original CDs and 6 months after treatment completion with new dentures; 25 patients received a mandibular CD and 38 received a mandibular IOD. Anterior ridge height at the mandibular symphysis was determined on lateral cephalograms to provide subgroups of low (= 21 mm), moderate (> 21 mm, 28 mm), and high (>= 28 mm) ridge height for both CDs and IODs. Masticatory performance tests on the preferred chewing side (PS) and swallowing threshold tests were made with peanuts and carrots. Results: Analysis of variance was used for comparisons of mean change in performance after treatment with study dentures for the 3 bone height groups; this indicated significant differences between the CD and IOD for PS masticatory performance with peanuts (P = .05) and carrots (P = .03). Post hoc tests found significant mean differences between the CDs and IODs with peanuts (P = .008) and carrots (P = .01) only in the low bone height group. Although no significant differences were found in swallowing threshold performance, the mean change scores for subjects with low bone height were greater with the IODs than those with CD for swallowing threshold performance, strokes, and time. Discussion: It is suggested that only in patients with advanced ridge resorption is the mandibular IOD more likely than a CD to result in improvements in masticatory performance. Conclusion: The study indicated that treatment with a mandibular IOD may improve masticatory performance only in persons with a less than adequate mandibular ridge.