<h3>Purpose/Objective(s)</h3> Non-small cell lung carcinoma (NSCLC) represents a diverse array of malignancies with the primary histologic subtypes of adenocarcinoma (ADC) and squamous cell carcinoma (SCC). Nearly one third of patients diagnosed with NSCLC will present with stage III disease. In patients with unresectable disease, the current standard is definitive chemoradiotherapy (CRT) followed by immunotherapy. Even though the systemic therapeutic landscape has changed based on histological subtype, radiation treatment remains the same for all NSCLC. Also it remains unclear whether certain clinicopathologic factors are associated with either histology or if histology influences survival outcomes following definitive CRT. Therefore, we analyzed the national cancer database (NCDB) to compare overall survival (OS) in Stage III NSCLC patients with ADC and SCC treated with definitive CRT. <h3>Materials/Methods</h3> We queried the NCDB for patients diagnosed with Stage III ADC or SCC of the lung between the years 2004 – 2015 who were treated non-surgically with concurrent CRT to a definitive dose (60-74 Gy). Univariable and multivariable analyses identified characteristics predictive of OS. Survival was calculated using Kaplan Meier method. Multivariable logistic regression was performed to identify clinicopathologic variables associated with each histology. <h3>Results</h3> Ultimately 17,015 Stage III NSCLC patients with either SCC (n=9,406) or ADC (n=7,609) were eligible for analysis. Univariable analysis demonstrated a median OS of 24 months and 20 months (p<0.0001) and 3-year OS rates of 36% and 30% (p<0.0001) in patients diagnosed with ADC and SCC, respectively. Patients with SCC were more likely to be older (OR: 1.14, 95% CI: 1.07-1.23), have higher comorbidity scores (OR: 1.60, 95% CI: 1.43-1.80), left sided tumors (OR: 1.23, 95% CI: 1.14-1.31), and T4 lesions [OR: 2.68, 95% CI: 2.40-2.99, (p<0.0001, for all)]. Patients with SCC were less likely to have N2 (OR: 0.83, 95% CI: 0.72-0.94) or N3 disease (OR: 0.53, 95% CI: 0.46-0.62) and to receive treatment at an academic treatment facility (OR: 0.90, 95% CI: 0.84-0.97). Younger age, lower comorbidity score, higher radiation dose (i.e. ≥ 70 Gy), female sex, lower T stage, lower N stage, and ADC histology were associated with improved OS on multivariable comparison (p<0.01, for all). <h3>Conclusion</h3> Compared to ADC, SCC was associated with higher T stage, lower N stage, older patients with greater comorbidity scores, and left sided tumors. Both median, as well as, 3-year and 5-year OS rates were inferior in patients with SCC compared to ADC. Prospective studies are needed to validate these findings and potentially identify radiotherapeutic strategies that may improve outcomes in this histologic subset.