Purpose: Short- or long-term implant survival and success are related to peri-implant marginal bone loss (MBL), among other key factors. The purpose of this study was to analyze the role of clinical and implant-related variables in MBL over a long-term follow-up. Materials and Methods: A retrospective study of 558 implants in 172 patients was conducted, analyzing the relationship between MBL and clinical, implant-related, and prosthetic design-related variables. MBL was measured on digital radiographs with specific software, using implant threads as reference. Results: Linear mixed analysis revealed the following significant effects: a lower mean MBL for type IV bone (0.047 mm/year, 95% CI [-0.019, 0.119]) than for type III bone (0.086 mm/year, 95% CI [0.038, 0.138]), type II bone (0.112 mm/year, 95% CI [0.070, 0.167]), or type I bone (0.138 mm/year, 95% CI [0.052, 0.23]); an increased MBL of 0.033 mm/year for each increment of 1 mm in diameter (95% CI [0.002, 0.065]); a lower mean MBL in smooth implants (0.103 mm/year, 95% CI [0.090, 0.117]) vs rough implants (0.122 mm/year, 95% CI [0.102, 0.142]). The mean MBL was > 0 mm/year for all prostheses except for fixed complete dental prostheses. Conclusion: Within the limits of a retrospective follow-up study, a lower mean peri-implant MBL was associated with type IV bone, a smaller diameter, a smooth surface, and a fixed complete dental prosthesis. Keywords: alveolar bone loss, bone tissue, dental implants, implant-supported dental prosthesis