Objective: The primary treatment for stage I non-small cell lung cancer (NSCLC) in medically inoperable patients is stereotactic body radiation therapy (SBRT). The current study aimed to retrospectively analyze patients who underwent SBRT. Methods: A total of 188 patients with stage I NSCLC treated with SBRT between 2014 and 2020 were enrolled. Local control (LC), progressionfree survival (PFS), overall survival (OS), and treatment-related toxicities were analyzed. Results: Patients were mostly male (65.7%, n=71), with a median age of 68 (56-88). Based on tumor size and location, 69 patients (63.9%) received between 50 and 60 Gy in 5 fractions, 26 patients (24.1%) received 54 Gy in 3 fractions, 11 patients (10.2%) received 60 Gy in 8 fractions, and 2 patients (1.8%) received 60 Gy in 3 fractions. The median follow-up time was 32 months (12-47 months). Locoregional relapse occurred in 11 patients, among whom 4 (3.7%) developed distant metastasis. The 3-year LC, OS, and PFS rates were 89.5%, 83%, and 72%, respectively. Advanced age and presence of chronic obstructive pulmonary disease were associated with a decreased 3-year OS. In smokers and those with large tumor volumes, PFS decreased to 3 years. No grade 3 or 4 treatment-related toxicities were observed. Conclusion: SBRT is a fast, safe, and valuable therapeutic approach for patients with early-stage medically inoperable NSCLC, providing significant tumor control rates with low toxicity.