Objective To investigate the value of sarcopenia in predicting the prognosis of advanced NSCLC patients using PD1 / PD-L1 immune checkpoint inhibitors ICIs and the incidence of immune - related adverse events irAEs . Method A total of 82 eligible patients with advanced NSCLC treated by PD1 / PD-L1 inhibitors in first-line second-line or third-line were enrolled from May 1 2019 to April 30 2022 at the affiliated Suzhou Hospital of Nanjing Medical University. Patients were divided into sarcopenia group and non- sarcopenia group based on SMI. All the follow - up data including skeletal muscle index SMI blood routine examination blood biochemical test and treatment response were collected in the electronic medical record system. Through Kaplan-Meier Cox survival analysis the Mann - Whitney U test the chi square test univariate and multiple Logistic regression analysis and an independent t-test we evaluated the value of sarcopenia in predicting the curative effect of ICI inhibitors for patients with advanced NSCLC. Result The median progression free survival PFS of all 82 enrolled patients was 8. 5 months range 0. 7-40 months 95%CI = 8. 16-11. 47 . The Kaplan-Meier analysis revealed that patients with sarcopenia had a significantly shorter PFS than those without sarcopenia 5. 8 vs 10 months P = 0. 017 . Mann-Whitney U test showed that triglyceride waist circumference nutritional risk screening 2002 NRS 2002 grade and Karnofsky performance score KPS were significantly different between the two groups P= 0. 022 0. 004 0. 009 0. 007 respectively . Patients were grouped according to whether they had an objective response,and it was found by independent t - test. There was a significant difference in ORR between the sarcopenia group and the non - sarcopenia group 5. 56% vs 39. 13% P = 0. 001 . Based on the occurrence of disease remission patients were categorized into a group of complete remission and partial remission referred to as the OR group and a group of stable disease and disease progression referred to as the non-OR group . An independent t-test revealed a significant difference in SMI between the OR group and the non-OR group 50. 24±8. 48 cm 2 / m 2 vs 45. 09±9. 82 cm 2 / m 2 P= 0. 0408 . The incidence of irAEs in the sarcopenia group was higher than the non-sarcopenia group P= 0. 015 . Moreover irAEs were associated with body mass index BMI albumin / globulin ratio A/ G triglyceride waist circumference third-line treatment and sarcopenia among which A/ G and third-line treatment were independent risk factors. Conclusion Sarcopenia can be used as a sensitive indicator to predict the prognosis of patients with advanced NSCLC receiving immunotherapy. It can effectively identify patients with a poor prognosis thus providing more detailed prognosis stratification and effectively guide clinical early intervention.