Background: There exists a strong relationship between cancer and inflammation. For this reason, attempts have been made to identify different biomarkers of inflammation in recent years. The neutrophil - lymphocyte ratio (NLR) a marker of systemic inflammation, and the infiltranting lymphocytes of the tumor stroma (TILs) have been studied by our research team in different tumors, such as melanoma, breast cancer, colon cancer and NSCLC in patient who had recieved tratment with chemotherapy. We could observe that there was a significant relationship beteween DFS and a high NLR on the one hand, and DSF an intense TILs on the other. Our main objective is to evaluate the relationship between the objective response rate (ORR) and the pretreatment NLR in patients with advanced NSCLC who recieved immunotherapy. Our secondary objective is to analyzed the associated between PFS and RNL in patients with advanced NSCLC undergoing immunotherapy. Methods: Patients with diagnosis of advanced-stage NSCLC who recieved only immunotherapy, immunotherapy with another immunomodulator or in combination with platinum-based chemotherapy werw included. All patients had a follow-up of at least 6 months. The cutoff value > or < 3 for the NLR was use to reference. The laboratory control prior to the beginning of treatment was taken, and the ORR was determined using the Response Evaluation Criteria In Solid Tumors (RECIST) criteria. Statistical analysis was performed using dispersion and position measurements, T-Test and Chi Square test. For PFS analysis Kaplan-Meyer was used. The level of significance for the variables was p < 0.05. Results: 41 patients with advanced NSCLC were analyzed. 43.9% (18 pts) recieved immunotherapy alone with nivolumab. 34.14% (14 pts) received a combined treatment (nivo / ipi) and 21.95% (9 pts.), immuno / QT combination (based on platinum). Regarding the histological presentation, 80.48% were adenocarcinoma. 54% (22 pts) had an NLR > 3 and 46% (19 pts) an NLR < 3. The ORR in the general population was 24%. in pts with an NLR < 3, the ORR that was observed was 42% vs. ORR of 9% in pts with NLR > 3 (p: 0.02). These differences were statistically significant. The median PFS was 11.27 months in the general population. As regards RNL, the median PFS were 20.74 vs 5.52 months in favor of pts with an NLR < 3 (p: 0.04). Conclusions: We could conclude that patients with NSCLC and pretreatment NLR < 3, who undergo immunotherapy, had better ORR compared to those with NLR > 3. These differences was statistically significant. Also, we could observe better PFS in patient with NLR < 3. These difference was estatically significant. We will keep working to obtain a greater number of patients. Then we could have a better analysis and statistical power. It is possible that NLR will be a highly useful and easy-to-acces predictive factor, and it could be used in patients with immunotherapy in our daily practice.