Purpose: The aim of this study was to compare the clinical outcomes of four-implant-supported overdentures retained by stud or bar attachments for patients with an edentulous maxilla. Materials and Methods: From January 2008 to December 2014, patients with maxillary edentulism were enrolled in this retrospective study. The insertion of four maxillary dental implants was followed by restoration with either stud-retained or barretained overdentures. The characteristics of the subjects and implants were recorded. Implant survival rates, marginal bone loss, peri-implant clinical parameters, prosthetic maintenance efforts, and patient satisfaction score were evaluated at the last follow-up time. The data were statistically analyzed, and the level of significance was set at α = .05. Results: A total of 132 implants were placed in 33 patients, of whom 18 were restored with four-implant-supported overdentures retained by stud attachments, and the other 15 with four-implant- supported overdentures retained by bar attachments. Thirty-one patients and 124 implants were available for the entire follow-up. During a mean follow-up period of 77 months (range: 36 to 111 months), five among 72 implants failed for three patients in the stud-retained group and two among 60 implants failed for two patients in the bar-retained group, resulting in estimated cumulative implant survival rates of 81.4% and 86.2% for the stud-retained group and the bar-retained group, respectively. Except for the modified Plaque Index (P = .035), no significant differences were indicated between the two attachment groups in terms of implant survival rate, marginal bone loss, peri-implant clinical parameters, or prosthetic maintenance treatment. Peri-/inter-implant gingival hyperplasia occurred only with implants under bar attachments. Patients in both groups reported a high degree of satisfaction. Conclusion: Within the limitations of this study, no significant differences were indicated between the clinical outcomes of maxillary four-implant-supported overdentures with either stud or bar attachments, although a higher modified Plaque Index was observed for the bar-retained group. Furthermore, prostheses with stud attachments were advantageous for their convenient cleaning and repair. Keywords: bar, dental implants, edentulous maxilla, overdenture, stud, survival rate