Purpose: In this prospective multicenter clinical study, 1,179 3i standard threaded and self-tapping implants were followed for up to 6 years and monitored according to established success criteria. Materials and Methods: A total of 493 patients (240 men and 253 women) with a mean age of 45.1 years at implant surgery were enrolled at 6 research centers after being screened for exclusion criteria. Implants were placed according to a 2-stage surgical protocol with a minimum of 4 months of submerged healing in the mandible and 6 months in the maxilla. Restorations included 633 prostheses, the majority of which were fixed partial dentures in the posterior mandible or maxilla or single-tooth replacements in the anterior maxilla. Results: One hundred four implants (8.8%) did not meet success criteria and were designated as failures, and 222 implants (18.8%) were lost to follow-up. The cumulative success rate according to life table methods was 91.1% at 6 years. Discussion: Sixty percent of the failed implants were short (= 10 mm long), and their cumulative success rate as a group at 6 years was 89.0%, compared to 93.1% for longer implants (P .05). Thirty-three percent of all failures were implants placed in the posterior maxilla, for a 5-year cumulative success rate of 87.4%. Conclusion: It appears that limited bone dimensions and poor-quality bone have an impact on the performance of these machined-surface implants.