Background: Lung cancer is the leading cause of cancer related deaths in the United States. Patients with advanced lung cancer tend to have varying degrees of protein energy malnutrition (PEM), due to multiple reasons including cancer related cachexia, sarcopenia, and adverse effect of chemotherapy. However, the impact of PEM on clinical outcomes in this subgroup needs further exploration. Methods: We utilized the 2020 National Inpatient Sample (NIS) Database in conducting this retrospective cohort study. We identified patients with lung cancer and PEM using appropriate ICD-10 diagnostic codes. We stratified patients with lung cancer based on the presence or absence of PEM. A survey multivariable logistic and linear regression analysis was used to calculate adjusted odds ratios (ORs) for the primary and secondary outcomes. A p value of <0.05 was considered statistically significant. The aim of this study was to investigate the impact of PEM on in-hospital mortality, hospital length of stay (LOS), and total hospitalization charge among hospitalized patients with lung cancer. Results: We identified a total of 92425 hospitalized patients with lung cancer, of which 10.53% (9739/92425) had comorbid PEM. The overall in-hospital mortality among patients with lung cancer was 5.79% (5360/92425). Among those with concomitant PEM, the mortality rate was significantly higher at 13.13% (1279/9739, p<0.001). Utilizing a stepwise survey multivariable logistic regression model that adjusted for patient and hospital level confounders, PEM was found to be an independent predictor of increased in-hospital mortality (adjusted OR 2.11; 95% (confidence interval [CI] 1.77-2.51; p<0.001), longer LOS (coefficient 3.02; CI 2.62-3.42; p<0.001), and higher total hospitalization charge (coefficient $22105; CI $13423- $30786; p<0.001). Conclusions: Our analysis demonstrated that PEM was widely prevalent in hospitalized patients with lung cancer and associated with worse outcomes. Efforts should be made to promote nutritional assessment and screening mechanisms with the aim to initiate early nutritional support as indicated. Further prospective studies are warranted to better understand these associations and guide management.