Background <p>Esophagectomy is associated with a high rate of postoperative pneumonia, which significantly impacts patient outcomes, including survival and quality of life. While some modifiable risk factors have been identified, the specific role of preoperative respiratory muscle function remains to be fully elucidated. Therefore, this study was designed to investigate the association of preoperative inspiratory muscle weakness (IMW) and respiratory sarcopenia (RS) with postoperative pneumonia in patients with esophageal cancer who underwent esophagectomy.</p> Methods <p>Patients with esophageal cancer who underwent esophagectomy between July 2021 and June 2023 were enrolled in this multicenter, retrospective, cohort study. The primary outcome was postoperative pneumonia, while preoperative IMW and RS were the main exposures. Respiratory sarcopenia was defined as the presence of both IMW and low skeletal muscle mass, which is assessed by using bioelectrical impedance analysis. Associations were analyzed by using G-computation within a Bayesian framework.</p> Results <p>A total of 213 patients were enrolled in this study. Postoperative pneumonia occurred in 42 patients (19.7%). Preoperative IMW was strongly associated with an increased risk of pneumonia, with a mean risk difference (RD) of 18.1% (95% credible interval [CrI] 5–33.6). The posterior probability that the RD exceeds 5% was &gt; 98%. Respiratory sarcopenia also showed a potential association, although with greater uncertainty (mean RD, 11.2%; 95% CrI − 3.8 to 27.9). The posterior probability that the RD exceeds 5% was 76.7%.</p> Conclusions <p>Preoperative IMW is a notable risk factor for postoperative pneumonia following esophagectomy. While a potential link with RS was found, its role remains uncertain and requires further investigation.</p>