Purpose: To compare marginal bone loss, soft tissue conditions, and prosthetic outcomes of implants supporting mandibular and maxillary bar-retained overdentures. Materials and Methods: A total of 124 implants (80 in the mandible and 44 in the maxilla) were placed in 35 patients. Bar-retained overdentures were fabricated for each patient. Prosthetic complications were recorded throughout the study. Plaque, peri-implant inflammation, bleeding, and calculus indices were recorded, and standard periapical radiographs were obtained at each implant site for measurement of marginal bone loss. Results: One implant failed in the mandible prior to prosthesis fabrication and one failed in the maxilla 5 years after prosthesis delivery. Both were replaced after 12 weeks of bone healing. The mean marginal bone loss around maxillary implants was greater than that around mandibular implants. Comparative evaluations of subgroups followed for 5 years and >= 5 years showed that soft tissue parameters were similar for maxillary and mandibular implants. One- and 5-year survival probabilities of the mandibular and maxillary overdentures were comparable. Kaplan-Meier and log-rank tests revealed that the probabilities of retightening of retainer and requirements for occlusal adjustments were higher for mandibular overdentures, whereas other maintenance requirements were comparable. The retainers in mandibular overdentures needed retightening more frequently than the retainers in maxillary overdentures. Conclusions: Dental implants supporting mandibular and maxillary bar-retained overdentures have similar peri-implant soft tissue outcomes and overall prosthetic survival probabilities. Keywords: bar retainer, complication, dental implant, overdenture, prosthodontics, soft tissue