Background: There is scarce data regarding the combined assessment of the costs and effects of implant treatments for edentulous patients when multiple options are available. Aim: This randomized clinical trial aimed to assess the cost-effectiveness of three different concepts for treatment: mandibular overdenture retained by a single (Group I; n=11) or two implants (Group II; n=13), and fixed hybrid prosthesis on four implants (Group III; n=13). Methods: Treatment effectiveness was measured as the 1-year before-after changes in patient satisfaction with the mandibular prosthesis. Costs were prospectively quantified from the perspective of the health provider, including all direct cost items attributed to the delivery of treatments and up to the 1-year follow-up, using a “bottom-up” costing estimation method. Results: Patient satisfaction after treatment improved significantly for the three groups. The overall costs were R$ 2,370.66, R$ 3,185.21, and R$ 5,739.52 for Groups I, II and III, respectively (p<0.001). Analysis of incremental cost-effectiveness ratios suggested that the overdentures retained by one or two implants, were more cost-effective than the fixed implant treatment, considering the mean cost and effectiveness values and the ±20% one-way sensitivity analysis. Conclusion: This study suggests that the incremental costs for the fixed hybrid prosthesis, compared to the overdenture treatments, is not proportional to the respective gain in effectiveness. Therefore, although all treatment options had satisfactory outcomes, the use of implants to retain a mandibular overdenture, irrespective of the use of one or two implants, is more cost-effective than the fixed implant treatment for the edentulous mandible.