The optimal fractionation schedule in unresected stage I non-small cell lung cancer (NSCLC) unsuitable for stereotactic body radiation therapy is unclear. Given the lack of comparative data regarding nonstereotactic body radiation therapy schemas, we compared overall survival (OS) with hypofractionated radiotherapy (HFRT) versus conventionally fractionated radiotherapy (CFRT) and examined the OS impact of different HFRT doses. This retrospective analysis included 2159 patients from the National Cancer Database diagnosed with stage I (cT1-2aN0M0) NSCLC between 2008 and 2016. Patients underwent CFRT (70≤BED10 biologically effective dose <100 Gy10 in ≥30 fractions), low-dose HFRT (LD-HFRT; 70≤BED10 assuming α/β=10 <100 Gy10 in 11 to 24 fractions), or high-dose HFRT (HD-HFRT; 100≤BED10 ≤120 Gy10 in 6 to 10 fractions). Patients who received surgery, chemotherapy, or immunotherapy were excluded. We compared CFRT versus all HFRT, and separately CFRT versus LD-HFRT and CFRT versus HD-HFRT. OS was evaluated with the Kaplan-Meier estimator, log-rank test, and Cox regression. A total of 63.2% of patients underwent CFRT, 23.5% LD-HFRT, and 13.3% HD-HFRT. OS was significantly longer with HFRT versus CFRT on univariable (28.2 mo 95% CI, 25.6-31.7 vs 26.4 mo 25.0-27.9; log-rank=0.0025) but not multivariable analysis (MVA; hazard ratio HR 0.90; P=0.062). MVA yielded no significant difference in OS between CFRT and LD-HFRT (HR 0.96, P=0.53). OS was significantly longer with HD-HFRT versus CFRT on MVA (HR, 0.75; P=0.003). However, on sensitivity analysis using different multivariable modeling techniques, this did not retain statistical significance (HR, 0.83; P=0.12). For stage I NSCLC, HFRT does not show a robust OS benefit compared with CFRT but may be preferred given the convenience and lower costs.