Purpose: In this retrospective study, marginal peri-implant bone height around machined and sandblasted/ acid-etched interforaminal implants in the mandible was evaluated radiologically at least 3 years after functional loading. Materials and Methods: Fifty-one patients, each with 4 interforaminal screw-type implants placed between 1994 and 1998, were included in this study. Of these, 36 patients (70.6%) with a total of 144 implants (76 machined Mk II implants and 68 sandblasted/acidetched Frios implants) were available for follow-up studies. Interforaminal marginal bone loss was evaluated by extraoral rotational panoramic radiographs. In addition, predictive factors such as patient age and sex, nicotine use, implant position, implant life, and site of measurement were recorded, as well as bone loss at surgery (ie, baseline bone loss). Analysis of covariance for repeated measurements was used for statistical analysis. Between-group differences were expressed as least square means ± standard error. Results: Sandblasted/acid-etched implants showed significantly less marginal bone loss than machine-surfaced implants (2.4 ± 0.23 mm vs 1.64 ± 0.27 mm). Implants placed in the anterior of the arch showed significantly more peri-implant bone loss than implants placed in the posterior (P = .0001). Discussion and Conclusions: Significantly less long-term peri-implant bone loss was observed for rough implant surfaces compared to machine-surfaced implants. However, it was also demonstrated that both types of implants, in combination with bar-supported overdentures, can produce excellent long-term results in the atrophic edentulous mandible. Mesially placed implants showed more bone resorption than distally positioned implants, independent of surface roughness.