Objective: The aim of the present prospective clinical study was to assess the survival rate and the radiologic crestal bone level alteration around four interforaminal immediately loaded narrow-diameter implants (NDIs) in the edentulous mandible. Method and Materials: A total of 20 participants received each 4 NDIs (MDI, 3M Espe; diameter 1.8 mm, length 13 or 15 mm) in the edentulous mandible. Immediate loading was performed if insertion torque was 35 Ncm or higher. The implants were loaded the same day by converting the existing full denture into an implant overdenture. Follow-up visits were performed five times (baseline to 52 weeks). Standardized radiographs were taken at baseline and 12, 26, and 52 weeks post-loading. Clinical parameters (Plaque Index, probing depth, bleeding on probing) were assessed. The nonparametric ANOVA test was used to assess crestal bone level changes. Results: In all 20 patients the healing of the total 80 implants was uneventful and no implant was lost. Sixty-eight (85%) implants were loaded immediately. All clinical parameters showed healthy, stable, and well-maintained peri-implant soft tissue conditions. The mean (± standard deviation) radiographic bone loss after 1 year was 0.78 (± 0.64) mm. Conclusion: According to the 1-year results of this prospective clinical study, NDIs seem to be a reliable alternative to support prostheses in edentulous patients with a reduced horizontal mandibular bone volume. Keywords: bone loss, edentulism, immediate loading, mandibular overdenture, narrow-diameter implants