This study investigated treatment patterns and outcomes in patients with inoperable stage III non-small cell lung cancer (NSCLC) treated with radiotherapy (RT) in Turkey. We included 492 patients with stage III NSCLC in this multi-center retrospective study. Pa-tient demographics, clinical characteristics, and clinical treatment patterns from the time of the initial diagnosis to disease progression were recorded. Additionally, the prognostic factors predicting overall survival (OS) and progression-free survival (PFS) were analyzed. For the initial treatment, 429 patients (89.2%) received chemotherapy and RT, whereas 53 patients (10.8%) were treated only with RT. The first disease progression occurred in 288 patients (58.4%) at 9.3 months (median) after the initial treatment, and 64.6% re-ceived treatment after first progression. The second disease progression occurred in 30 patients, and 20 patients (66.7%) received treatment. Median OS and PFS were 27.0 months and 13.4 months, respectively. Age (p< 0.001), stage (p= 0.04), poor performance score (PS) (p= 0.03) and RT doses (p= 0.002) were independent predictors for OS and PFS in our multivariate analysis. Additional significant predictors for OS in the multivariate analysis were gender (p= 0.004), treatment period (0.02), and irradiation technique (p= 0.02). Disease progression occurred in nearly 58% of the patients, and one-third of these patients remained untreated during the disease progression. These findings indicate a need for additional treatment options in patients with unresectable stage III NSCLC with high-risk features, namely older age, stage IIIB disease, poor PS, and lower RT doses.