Aim: Lung cancer is the most common cause of cancer- related deaths in the world. Diabetes mellitus (DM) can be seen frequently in the lung cancer patient group as well as in the normal population. Metformin is one of the most commonly used biguanide drugs in the treatment of DM. Studies conducted in patients with different types of cancer, such as breast, liver, and prostate, have shown that metformin use may contribute to survival. The aim of the study is to evaluate the effect of metformin on survival in patients with non-small cell lung cancer (NSCLC). Matherial and Methods: In this study, 85 patients diagnosed with non-small cell lung cancer and concurrent type 2 DM retrospectively were analyzed, and the last follow-up date was 31.11.2020. Neutrophil/lymphocyte ratio (NLR) of the patients was calculated. Alkaline phosphatase (ALP), lactate dehydrogenase (LDH), carcinoembryonic antigen (CEA) values and their contribution to survival were examined. Results: The 1, 3, and 5-year overall survival rates for all patients were 76.0%, 46.5%, and 34.3%, respectively, and the median OS was 64.1 (95% CI: 44.7-83.5). Lymph node (LN) positivity, liver metastasis, and death rates were less common in the patient group receiving metformin. Overall survival (OS) results and determined survival rates were worse in the non-metformin patient group. Conclusion: Metformin usage and the control of hyperinsulinemia and hyperglycemia may contribute to survival rates. Larger and prospective studies are needed to determine the effect of metformin which is used for glycemic control and insülin resistance, in NSCLC patients' survival.