Background <p>This study investigates the association between preoperative dehydration and 30-day postoperative complications following aseptic revision total shoulder arthroplasty (TSA).</p> Methods <p>The American College of Surgeons National Surgical Quality Improvement Program database was queried for all patients who underwent aseptic revision TSA from 2015 to 2022. The study population was divided into two groups based on preoperative hydration status: normal (blood urea nitrogen (BUN)/creatinine (Cr) &lt; 25) and dehydration (BUN/Cr ≥ 25). Logistic regression analysis was conducted to investigate the relationship between preoperative dehydration and postoperative complications.</p> Results <p>Compared to normal hydration, dehydration was associated with a significantly greater likelihood of experiencing any complication (<i>P</i> = 0.004), nonhome discharge (<i>P</i> = 0.002), and length of stay (LOS) &gt; 2&#xa0;days (<i>P</i> &lt; 0.001). After controlling for potential confounding variables with multivariate analysis, dehydration was independently significantly associated with LOS &gt; 2&#xa0;days (odds ratio 1.50, 95% confidence interval 1.05–2.14; <i>P</i> = 0.028).</p> Conclusion <p>Preoperative dehydration status is associated with a greater rate of early postoperative complications and is an independent predictor of LOS exceeding two days following aseptic revision TSA. A better understanding of dehydration as a risk factor for postoperative complications may help surgeons better select surgical candidates and improve surgical outcomes in the setting of aseptic revision TSA.</p> Level of evidence <p>Level III; Retrospective Cohort Comparison; Prognosis Study.</p>