Nine clinical centers using the Branemark System participate in a prospective study of 159 partially edentulous patients between 18 and 70 years of age. Clinical parameters evaluated were Plaque Index, gingivitis, pocket depth, Bleeding Index, tooth mobility, prosthesis stability, and stomatognathic function. Change in bone height around fixtures was measured radiographically. After 3 years, 460 loaded fixtures, supporting 174 prostheses in 139 patients, remain in the study. The complications, failures, and technical problems are presented. After 3 years of this 5-year study, results suggest that implant-based treatment of partially edentulous patients may achieve a success rate comparable to that obtained in edentulous patients.