This study was designed to compare the results of immediate and delayed loading of implants with implant-retained mandibular overdentures. Ten patients (test group) received 40 Brånemark System MKII implants (4 per patient) placed in the interforaminal area of the mandible. Standard abutments were immediately screwed to the implants, rigidly connected with a bar, and immediately loaded with an overdenture. Ten patients (control group) received the same type and number of implants in the same area, but the implants were left to heal submerged. Four to 8 months later, standard abutments were screwed to the implants and the same prosthetic procedure was applied. Each implant was evaluated at the time of prosthetic loading and at 6, 12, and 24 months after the initial prosthetic load with the following parameters: modified Plaque Index (MPI), modified Bleeding Index (MBI), probing depth (PD), and Periotest. Peri-implant bone resorption was evaluated on panoramic radiographs taken 12 and 24 months after initial prosthetic loading. No significant differences were found between the 2 groups regarding MPI, MBI, Periotest, peri-implant bone resorption, and PD at 6 and 24 months (P > .05). The only difference was found regarding PD values on the mesial and lingual sites at 12 months (P .05). The cumulative success rate of implants was 97.5% in both groups. Results from this study showed that immediate loading of endosseous implants rigidly connected with a U-shaped bar does not seem to have any detrimental effect on osseointegration. Conversely, this method significantly shortens the duration of treatment with relevant satisfaction for the patients. Keywords: endosseous dental implants, immediate loading, implant overdenture