Purpose To compare survival rates of thermal ablation and stereotactic radiation therapy (SRT) for stage 1 non-small cell lung cancer (NSCLC). Materials and Methods In this retrospective study, patients with stage 1 NSCLC treated by thermal ablation (TA) or SRT were identified in the 2004-2013 National Cancer Database. Patients who underwent TA and SRT were one-to-one propensity matched to undergo thermal ablation. Outcomes were overall survival and unplanned hospital readmission within 30 days after treatment. Results This study included 28 834 patients (TA, 1102 patients; SRT, 27 732 patients). Patients treated with TA had more comorbidities (Charlson comorbidity index of 1 vs ≥2, 32.8% [362 of 1102] vs 19.7% [217 of 1102], respectively) compared with SRT (Charlson comorbidity index of 1 vs ≥2, 26.9% [7448 of 27 732] vs 15.3% [4251 of 27 732], respectively; P , .001) and smaller tumor size (mean tumor size, TA vs SRT: 19 mm vs 22 mm, respectively; P , .001). In the propensity score-matched cohort with balanced distribution of potential confounders, there was no significant difference in overall survival between TA and SRT at a mean follow-up of 52.4 months (survival difference, P = .69). Overall survival rates were comparable between TA and SRT (1 year, 85.4% vs 86.3%, respectively, P = .76; 2 years, 65.2% vs 64.5%, respectively, P = .43; 3 years, 47.8% vs 45.9%, respectively, P = .32; 5 years, 24.6% vs 26.1%, respectively, P = .81). Unplanned hospital readmission rates were higher for patients who underwent TA versus those who underwent SRT (3.7% [40 of 1070] vs 0.2% [two of 1070], respectively; P , .001). Conclusion Regarding overall survival, thermal ablation was noninferior to stereotactic radiation therapy for primary treatment of stage 1 non-small cell lung cancer. © RSNA, 2018 Online supplemental material is available for this article. See also the editorial by Shyn in this issue.