Purpose: To evaluate and compare the implant survival rate, marginal bone levels, and prosthesis failure rate of a three-unit fixed dental prosthesis (FDP) supported with three or two implants immediately loaded in the posterior area. Materials and Methods: Partially edentulous patients in need of a three-unit implant-supported FDP in the maxillary/mandibular posterior region were recruited and randomly split into two groups: a control group with three-unit FDPs supported by three implants (3I group), and a test group with three-unit FDPs supported by two implants (2I group). Implants were inserted and immediately loaded with a temporary FDP. Results: In total, 63 patients were included in the study. A total of 178 implants were placed and immediately loaded (128 maxillary and 50 mandibular) to support 74 immediate provisional fixed prostheses (52 maxillary and 22 mandibular) delivered on the same day of implant placement: 30 in 3I group and 44 in 2I group. The comparison of three vs two implants resulted in comparable implant survival rates, marginal bone loss (MBL), and prosthesis failure rates. All implants healed uneventfully with no adverse clinical and radiographic signs or symptoms except for one implant failure in the 3I group resulting in a cumulative success rate of 99.5%—98.9% for the 3I group and 100% for the 2I group—with a follow-up of 6 to 10 years (mean: 7 years). Once loaded, the implants remained in function from a minimum of 6 years to 10 years. Conclusions: Although more studies and larger sample sizes are needed to validate this study, the results showed no difference between the two groups, demonstrating the potential viability of both clinical options.