Purpose: Conventionally, in patients with completely edentulous mandibles, fixed prostheses have been supported by four or more implants. However, an alternative protocol employing three implants and immediate loading has been developed. The objective of the present study was to assess the rehabilitation of edentulous patients treated with a complete fixed mandibular prosthesis with immediate loading and supported by three implants. Materials and Methods: In this observational study, a total of 99 implants placed in 33 patients was evaluated after 18 months in use. Panoramic radiographs were digitized to measure bone loss at the mesial and distal surfaces of each implant. Results: Mean peri-implant bone loss was 0.66 ± 0.51 mm for the left implant, 0.92 ± 0.61 mm for the central implant, and 0.82 ± 0.53 mm for the right implant. The bone loss observed around the distal implants was similar to that seen around the central implant, and there were no statistically significant differences in peri-implant bone loss between the three implant locations. There was no significant correlation between implant length and bone loss. The results were compatible with the peri-implant bone loss that has been described for prostheses of the same type supported by larger numbers of implants. Conclusions: The use of a complete fixed mandibular prosthesis with immediate loading supported by three implants proved to be an adequate option for the rehabilitation of edentulous patients. The protocol allowed simplification of treatment while maintaining similar bone loss to that reported for the same type of treatment supported by a larger number of implants. Palabras clave: dental implants, edentulism, implant-supported dental prosthesis, mandibular prosthesis