Background: Extra-short dental implants have emerged as a reliable option for rehabilitating posterior areas with limited vertical bone availability. However, clinical evidence regarding their use as single-unit restorations under immediate loading protocols in the mandibular first molar region remains scarce. Purpose: To evaluate implant survival, marginal bone loss, and biological and prosthetic complications associated with single extra-short implants (5.5 and 6.5 mm) immediately loaded in the mandibular first molar position. Materials and Methods: A retrospective study was conducted including 19 patients rehabilitated with 19 extra-short implants placed in the mandibular first molar region between June 2019 and June 2023. All implants were restored with single screw-retained crowns on a unitary transepithelial abutment and immediately loaded within 24 hours. Implant survival and marginal crestal bone loss were assessed radiographically. The mean follow-up period was 38.6 ± 10.5 months. Results: No implant or prosthetic failures were recorded during the follow-up period, resulting in a cumulative survival rate of 100%. Mean marginal bone loss was 0.36 ± 0.13 mm mesially and 0.60 ± 0.16 mm distally. No clinically relevant biological complications were observed. Conclusions: Within the limitations of this retrospective study, immediately loaded single extra-short implants placed in the mandibular first molar region demonstrated favorable clinical outcomes. Careful case selection, conservative surgical protocols, and standardized prosthetic design appear to be key factors for achieving predictable results in this demanding clinical scenario.