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Although obesity is associated with increased complication rates after lower-extremity arthroplasty, there is a relative paucity of studies examining the effect of body mass index (BMI) on shoulder arthroplasty. The purpose of this investigation was to evaluate the effect of BMI on implant survival and the rate of complications after shoulder arthroplasty.Using an institutional total joint registry, 4,567 consecutive shoulder arthroplasty cases from 1970 to 2013 were studied. The mean BMI was 29.7 kg/m2 (range, 14 to 66 kg/m2), with 1,622 patients (36%) with a BMI of 30 to 40 kg/m2 and 297 patients (7%) with a BMI of >40 kg/m2. There were 2,493 female patients (55%). BMI was dichotomized after examination of the smoothing spline curve. The associations of factors and complications were assessed using Cox proportional hazard regression analysis.Increasing BMI was associated with an increased risk of a revision surgical procedure, reoperation, revision for mechanical failure, and superficial infection, and it was negatively associated with risk of a periprosthetic fracture. The risk of a revision surgical procedure increased in a linear fashion with increasing BMI (hazard ratio [HR], 1.05, or a 5% increased risk per 1 unit of BMI; p = 0.03). Increased BMI was also associated with an increased risk of revision for mechanical failure (HR, 1.05; p = 0.004). In a multivariate model, the association of BMI and risk of a revision for any reason, revision for mechanical failure, and reoperation maintained significance (p ≤ 0.02). The most marked association between increasing BMI and any complication in shoulder arthroplasty was its association with superficial wound infection (HR, 1.09; p = 0.03).Increasing BMI is strongly associated with increased rates of revision surgical procedures and postoperative complications after shoulder arthroplasty. It is important to consider these findings when counseling patients, estimating risks, and estimating complication risks in policy decisions.Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.