['To determine the frequency and clinical significance of epidermal growth factor receptor (EGFR) mutations in patients with potentially curable stage III non-small-cell lung cancer (NSCLC) who are eligible for definitive chemoradiotherapy (CRT).', 'Between January 2001 and December 2010, we analyzed the EGFR mutational status in consecutive NSCLC patients who were treated by CRT. The response rate, relapse-free survival, 2-year relapse-free rate, initial relapse sites, and overall survival of the patients were investigated.', 'A total of 528 patients received CRT at our hospital during the study period. Of these, 274 were diagnosed as having nonsquamous NSCLC. Sufficient specimens for mutational analyses could be obtained from 198 of these patients. The proportion of patients with EGFR activating mutations was 17%. In addition to the well-known characteristics of patients carrying EGFR mutations (female, adenocarcinoma, and never/light smoker), the proportion of cases with smaller primary lesions (T1/2) was found to be higher in patients with EGFR mutations than in those with wild-type EGFR. Patients with EGFR mutations showed similar response rate, relapse-free survival, and 2-year relapse-free rates as compared to patients with wild-type EGFR. Local relapses as the site of initial relapse occurred significantly less frequently in patients with EGFR mutation (4% vs 21%; P=.045). Patients with EGFR mutations showed longer local control (adjusted hazard ratio 0.49; P=.043). After disease progression, a majority of the patients with EGFR mutations received EGFR tyrosine kinase inhibitors (62%), and these patients showed longer postprogression survival than those with wild-type EGFR.'] Is epidermal growth factor receptor mutation associated with longer local control after definitive chemoradiotherapy in patients with stage III nonsquamous non-small-cell lung cancer?