Metabolic syndrome can adversely affect surgical outcomes. This study evaluated the postoperative outcomes of patients with metabolic syndrome after total shoulder arthroplasty (TSA). A retrospective cohort study of 4751 patients undergoing TSA was conducted with use of the American College of Surgeons National Surgical Quality Improvement Program database from 2005 to 2013. Metabolic syndrome was defined as hypertension, diabetes, and body mass index of 30.0 kg/m2 or greater. Multivariable logistic regression analysis was performed for the outcomes of any postoperative complications and extended length of stay. Patients classified as obese III had a significantly increased risk of extended length of stay (P=.011) compared with control subjects who were of normal weight. In the multivariable adjusted models, compared with nonobese patients, those classified as obese I and obese II had a significantly decreased risk of postoperative complications (odds ratio, 0.84, P=.020, and odds ratio, 0.82, P=.045, respectively), whereas those classified as obese I were less likely to have extended length of stay (odds ratio, 0.79, P=.004). Metabolic syndrome was not a significant predictor of postoperative complications or extended length of stay. Morbidly obese patients undergoing TSA have an increased risk of postoperative complications and extended length of stay. Those classified as obese I and obese II may have a decreased risk of postoperative complications and shorter length of stay. Despite the hypothesized negative effect of metabolic syndrome on outcomes, the overall effect of metabolic syndrome was insignificant. These results are consistent with previous studies on obesity in patients undergoing TSA and may explain why recent studies have not shown differences in the rate of complications after TSA in obese patients with a body mass index of 30 to 40 mg/kg2.