Background: Despite approvals of immune checkpoint inhibitors in both small cell and non-small cell lung cancers, role of immunotherapy in large cell neuroendocrine carcinoma (LCNEC) in lung is undefined. Methods: Using National Cancer Database (NCDB), Stage IV LCNEC cases diagnosed in 2014-2016 with at least 30-day follow up were analyzed. Clinical demographics included age (20-69 vs. 70+), sex (male vs. female), race (whites vs. others), insurance (uninsured vs. others), institution (academic vs. others), Charlson-Deyo score (0-1 vs. 2-3), brain metastasis (Yes vs. No), liver metastasis (Yes vs. No). Information regarding cancer treatment was limited to first course of therapy, including surgery for primary lesion (Yes vs. No), radiation (Yes vs. No), chemotherapy (Yes vs. No), and immunotherapy (Yes vs. No). Survival analysis was performed using Kaplan-Meier curves and Log-rank tests. Cox proportional hazard model was used for multivariate analyses. A two-sided p-value < 0.05 was considered as significant. Results: Among 661 eligible cases, 37 patients were treated with immunotherapy. No significant association between use of immunotherapy and clinical demographics was observed except for use of chemotherapy (p = 0.0008). Chemotherapy was administered in 34 (92%) and 406 (65%) of cases in immunotherapy and non-immunotherapy groups, respectively. Use of immunotherapy was associated with improved overall survival (Log-rank p = 0.0168). Landmark analysis in the immunotherapy group showed 12 and 18-month survival of 34.0% and 29.1%, respectively, as compared with 24.1% and 15.0% in the non-immunotherapy group Multivariate analysis demonstrated that female sex, presence of liver metastases, surgery, use of chemotherapy and immunotherapy (HR = 0.64, p = 0.0164) had significantly improved survival. Propensity score matching in overall survival showed a nonsignificant trend (p = 0.0733) in favor of immunotherapy group. Conclusions: This retrospective study using one of the largest cancer databases suggests that use of immunotherapy may improve survival of LCNEC patients. Prospective studies are warranted for further validation.