Objective:To evaluate the impact of sarcopenia on survival and treatment-related toxicity in postoperative recurrent esophageal squamous cell carcinoma (ESCC) patients treated with chemoradiotherapy.Methods:Clinical data of 147 patients with postoperative locoregional recurrent ESCC receiving chemoradiotherapy in Huai'an First People's Hospital from 2016 to 2017 were retrospectively analyzed. Pectoralis muscle area (PMA) was determined using routine pre-radiotherapy CT simulation scan above the aortic arch level. Sarcopenia was defined as a cut-off value of pectoralis muscle index (PMI) (PMA/height 2) <11.55 cm 2/m 2 for males and <8.69 cm 2/m 2 for females. The incidence of toxicity, 1- and 3-year overall survival (OS) rates were statistically compared between patients with and without sarcopenia. Results:Sarcopenia was detected in 49 of 147 (33.3%) patients. The incidence of grade 3-4 toxicities in sarcopenic patients was significantly higher compared to that in their counterparts without sarcopenia (40.8% vs. 18.4%, P=0.005). In addition, patients with sarcopenia had significantly worse 1-year (61.2% vs. 82.7%) and 3-year OS rates (10.2% vs. 28.6%) than those without sarcopenia (both , P<0.001). Multivariate analysis showed that sarcopenia was an independent prognostic factor for poor OS ( P<0.001). Conclusion:PMI based on CT simulation scan has prognostic value in postoperative locoregional recurrent ESCC patients treated with chemoradiotherapy, which probably serves as a novel diagnostic tool for sarcopenia.