Introduction. SMARCA4/BRG1 loss of expression occurs in 5–10% of non-small cell lung carcinomas (NSCLC). We investigated the pathological, molecular and immune environment characteristics of this deficiency among NSCLC, its impact on overall survival (OS) of resected patients and the sensitivity to anti-PD1 inhibitors in metastatic patients. Materials and methods. BRG1 expression was assessed by immunohistochemistry to identify SMARCA4-deficient NSCLC (SD-NSCLC) from the cancer tissue collection of Cochin Hospital (Paris, France). Molecular profiles were analyzed by targeted NGS covering 28 genes in 63 resected SD-NSCLC. The balance of immune cells between CD8+, FOXP3+ cells and neutrophils (CD66b+) was characterized by multiplex immunohistochemistry and compared to non-SD NSCLC. Clinical outcome after anti–PD-1 therapy was evaluated in 7 SD-NSCLC out of 77 NSCLC patients. Results. SD-NSCLCs were more commonly found in TTF1-negative high-grade adenocarcinomas and pleomorphic carcinomas. They were associated with few targetable alterations (KRAS G12C and MET amplification). Their immune environment was characterized by an increased of FOXP3+ cell and neutrophil densities, but not of CD8+ T cells, compared to non-SD NSCLC. SD-NSCLC patients had a significantly shorter OS in early stages of resected patients and in metastatic patients treated by anti-PD1 treatment. Conclusion. BRG1-loss in NSCLC confers a poor prognosis and is associated with an immunosuppressive environment that could be responsible of limited efficacy to anti-PD1 inhibitors. The identification of SD-NSCLC by BRG1 immunohistochemistry is desirable for an optimal management of NSCLC patients.