relationship, and patients with higher body mass index (BMI), obese or overweight, have improved survival. BMI is the ratio between the weight in kilograms and the height in meters squared and is commonly used as surrogate for body composition. Using the BMI, obesity is defined as a BMI 30 Kg/m 2 , of overweight as a BMI between 25 and 29,9 Kg/m 2 , normal weight as a BMI from 18,5 to 24,9 Kg/m 2 and underweight below 18,5 Kg/m 2 . The objective of this study was to analyze the BMI of the patients with Non-Small Cell Lung Cancer (NSCLC) and to investigate its impact on overall survival. Methods: We conducted a retrospective analysis of patients diagnosed with metastatic non-small cell lung cancer diagnosed between 2000 and 2019, at AC Camargo Cancer Center, Brazil. Demographics, clinical-pathological characteristics, treatment patterns and outcomes data were obtained from electronic medical records. We collected weight and height information to calculate the BMI. Other variables such as ECOG, Charlson's comorbidity score, histological subtype, smoking load and number of metastasis were also analyzed. Overall survival was defined as the time between diagnosis and death by any cause. We used descriptive statistics to characterize the study population. Association between BMI and other variables was tested with Pearson's Chi-Squared or Fisher's exact tests. The Kaplan-Meyer method was used to estimate survival. Impact of BMI on survival was calculated with Cox regression method. P-values <0.05 were considered statistically significant. Results: We analyzed data from 456 patients with metastatic NSCLC. About 52,9% were men, 73,9% were white, 21,9% were smokers, 42,1% were former smokers and 32,2% non-smokers. Most of the patients had adenocarcinoma (78,5%). 63,2% of patients had 2 sites of metastasis. Median Charlson's score was 8 and 46,7% had ECOG 1. Median BMI was 24,3 kg/m2 (13,0-50,8). Patients were dichotomized into two groups based on the median BMI: <24,3 (89,7%) and 24,3 (10,3%). At a median follow up of 41,5 months, the median overall survival of the group who had lower BMI was 15,8 months versus 24,3 months in the group with higher BMI (HR¼1,56; 95% IC 1,0-2,3; P-value¼0,034). Conclusion: According to our data, there is an inverse relation between BMI and risk of death in patients with metastatic NSCLC. Patients who had lower BMI had a worse overall survival. BMI is associated with survival and should be considered as a prognostic factor in patients with lung cancer.