Background: Prior studies have demonstrated that neutrophil-lymphocyte ratio (NLR) can predict overall survival in patients undergoing stereotactic body radiation therapy (SBRT) for multiple types of cancer. The role of neutrophil-lymphocyte ratio (NLR) as a predictor for survival in single fraction SBRT-treated non-small cell lung cancer (NSCLC) patients remains unclear. Methods: A single-institution database of peripheral early-stage NSCLC patients treated with SBRT from February 2007 to May 2022 was queried. Consecutive patients with peripheral early-stage NSCLC (T1-2N0M0) and a complete blood count within six months of the start of SBRT treatment were included. Patients treated with SBRT regimens of more than 3 fractions were excluded as these regimens were reserved for patients with centrally located lesions with higher risk of toxicity which could affect survival. Optimal threshold of neutrophil-lymphocyte ratio (NLR) was defined based on maximally selected rank statistics. Cox multivariable analysis (MVA), Kaplan-Meier, and propensity score matching were performed to evaluate outcomes. Results: A total of 286 patients (164 female [57.3%]; median [IQR] age 76 [69-81] years) were included for analysis with median follow up of 19.7 months. The median NLR was 3.06 ([IQR] 2.21-4.33). There were 15 local failures, 27 nodal failures, and 50 distant failures. On Cox multivariate analysis, as a continuous variable, NLR was shown to be an independent predictor of OS (adjusted hazards ratio [aHR] 1.06, 95% CI 1.02-1.10, p = 0.005; Figure 1) and PFS (aHR 1.05, 95% CI 1.01-1.09, p = 0.013; Figure 1). In addition, NLR was associated with DF (aHR 1.11, 95% CI 1.05-1.18, p < 0.001; Figure 1). Maximally selected rank statistics determined 3.28 as the cutoff point of high NLR versus low NLR. These findings were confirmed upon propensity matching. Conclusions: Pretreatment NLR is an independent predictor for survival outcomes of peripheral early-stage NSCLC patients after SBRT. High NLR is associated with worse overall survival, progression-free survival, and distant metastasis. Pretreatment NLR levels should be tracked on trials for early-stage NSCLC patients.