Purpose: The investigators sought to determine whether maxillary sinus augmentation (MSA) was an independent risk factor for implant failure. Materials and Methods: Using a retrospective cohort study design, the investigators enrolled a sample composed of subjects having 1 or more implants placed in the posterior maxilla. The primary predictor variable was MSA status at the time of implant placement (MSA present or absent). MSA consisted of a lateral window (external) or an osteotome (internal) procedure. The outcome variable was implant failure defined as implant removal. Demographic, health status, anatomic, implant-specific, abutment-specific, prosthetic, and perioperative variables were also examined. Overall implant survival was estimated using Kaplan-Meier analysis. Risk factors for implant failure were identified using Cox proportional hazard regression models. Results: The sample consisted of 318 patients and 762 posterior maxillary implants. The mean duration of follow-up was 22.50 ± 19.06 months. The 5-year survival rates for implants in the ungrafted and grafted posterior maxilla were 88.0% and 87.9%, respectively (P = .08). After adjustment for covariates, MSA status was not an independent risk factor for implant failure (P = .9). Tobacco use (P .001), implants replacing molars (P .001), and 1-stage implants (P .001) were statistically associated with an increased risk for implant failure. Discussion: MSA status was not associated with implant failure risk. This finding may be subject to selection bias, as successful MSA was requisite prior to implant placement. Conclusion: MSA status was not associated with an increased risk for implant failure. Of the 3 factors associated with an increased risk for failure, tobacco use and implant staging may be modified by the clinician to enhance outcome. (Retrospective Clinical Cohort Study) (More than 50 references) Schlagwörter: implant failure, retrospective cohort studies, risk factors, sinus augmentation