Purpose@#The optimal treatment for patients with stage III non-small cell lung cancer (NSCLC) remains controversial. This study aimed to investigate prognostic factors and clinical outcome in stage III NSCLC using real-world clinical data in the Korean population. @*Materials and Methods@#Among 8,110 patients with lung cancer selected from 52 hospitals in Korea during 2014-2016, only patients with stage III NSCLC were recruited and analyzed. A standardized protocol was used to collect clinical information and cox proportional hazards models were used to identify risk factors for mortality. @*Results@#A total of 1,383 patients (46.5% had squamous cell carcinoma and 40.9% had adenocarcinoma) with stage III NSCLC were enrolled, and their median age was 70 years. Regarding clinical stage, 548 patients (39.6%) had stage IIIA, 517 (37.4%) had stage IIIB, and 318 (23.0%) had stage IIIC. Pertaining to the initial treatment method, the surgery group (median survival period: 36 months) showed better survival outcomes than the non-surgical treatment group (median survival period: 18 months, p=0.001) in patients with stage IIIA. Moreover, among patients with stage IIIB and stage IIIC, those who received concurrent chemotherapy and radiation therapy (CCRT, median survival period: 24 months) showed better survival outcomes than those who received chemotherapy (median survival period: 11 months), or radiation therapy (median survival period: 10 months, p<0.001). @*Conclusion@#While surgery might be feasible as the initial treatment option in patients with stage IIIA NSCLC, CCRT showed a beneficial role in patients with stage IIIB and IIIC NSCLC.