The aim of this study was to evaluate the clinical performance of the implants supporting mandibular overdentures, and to investigate the prosthodontic outcomes of the mandibular implant overdentures. Twenty edentulous patients participated in this study. Forty implants were placed in the canine areas of the mandibles of all patients using the 1-stage approach. New maxillary complete dentures and the mandibular implant overdentures were delivered to 10 patients in the test group 1 week after surgery, while new maxillary and mandibular complete prostheses were delivered to 10 patients in the control group. These conventional mandibular prostheses were converted to mandibular implant overdentures 3 months after surgery. No implants were lost neither in test nor in control group. The average ISQ values between the two groups were not statistically significant during 2 years (P > 0.05). The average marginal bone resorptions were 0.4 and 0.5 mm for the test and the control group after 2 years. The number of appointments required for the prosthodontic maintenance of the mandibular implant overdentures in the first year was higher than that in the second year, which was statistically significant(P < 0.001). The results of the study suggest that the 1-week early loading approach does not adversely influence the clinical performance of the implants supporting mandibular overdentures.