Background: Use of immune checkpoint inhibitors against advanced stage NSCLC is associated with significant reduction in overall morbidity and mortality. However, despite the survival benefit, tumors invariably relapse. We aim to study pattern of disease progression and assess baseline or tumor specific associations. Methods: We performed a retrospective review of 74 Veterans with Stage IV NSCLC who received ≥2 immunotherapy cycles between 2015-2021 at Albany Stratton VA Medical Center. IRB approval was obtained. Fisher Exact Probability Test was used to analyze data, level of significance at < 0.05. Results: Baseline characteristics of 74 male veterans revealed median age 67 years (IQR 62.5-72.5). Common tumor histology included squamous cell carcinoma (SCC; n = 38, 51.3%) and adenocarcinoma (n = 32, 43.24%), PD-L1 expression > 50% in 33.8% of population. Molecular testing positive for EGFR in 1 patient and otherwise negative for EGFR, ALK, BRAF, ROS, KRAS translocations in all patients. Treatment regimen was either immunotherapy alone or concurrent chemoimmunotherapy. Disease status prior to starting immunotherapy was classified as M1a (25.7%), M1b (50%) and M1c (24.3%). Out of total study population, progression of disease was noted in 48 patients (56.4%) further divided into progression at initial site only 20.8%, new site only 31.2%, or combined 48%. Most common sites of progression included local and distant LNs, brain, bone, and liver. Using Kaplan Meier Survival Analysis, median progression free survival (PFS) from start of immunotherapy till evidence of progression was 8.4 months. Our data revealed that progression at initial, new, and combined sites was noted in both adenocarcinoma and SCC. Use of immunotherapy as first line therapy and smoking history > 50ppd were also associated with risk of progression. Other characteristics such as ECOG score (p = 0.50), initial metastatic status (p = 0.30), type of immunotherapy (p = 0.60) and PD-L1 score (p = 0.27) did not reveal significant association. We did not find any association between baseline characteristics and improved PFS. Conclusions: We conclude that certain baseline characteristics can be associated with progression of Stage IV NSCLC on immunotherapy amongst Veteran population. We recommend further studies with a larger study population to analyze the pattern of disease progression and associated factors. This will allow physicians to modify and personalize therapy regimen to improve PFS.