Background Adjuvant chemotherapy after radical resection of stage IIIA non-small-cell lung cancer (NSCLC) has quite poor outcomes. We aimed to investigate whether adjuvant erlotinib therapy improves 2-year disease-free survival compared with chemotherapy in epidermal growth factor receptor (EGFR) mutation-positive stage IIIA NSCLC. Methods In this randomised, open-label, phase 2 trial, eligible patients aged 18-75 years who had undergone complete (RO) resection of histologically or pathologically confirmed stage IIIA EGFR mutation-positive NSCLC and had not received any previous anticancer therapies were enrolled. Patients were randomly assigned (1:1) to receive either adjuvant erlotinib (150 mg once daily administered orally) or vinorelbine and cisplatin chemotherapy (four cycles of vinorelbine [25 mg/m(2) intravenously on days 1 and 8 of each 21-day cycle] plus cisplatin [75 mg/m(2) intravenously on day 1 of each 21-day cycle]). Randomisation was done by Simon's minimisation with a random element and was stratified by EGFR activating mutation type (exon 19 vs 21), histology (adenocarcinoma vs non-adenocarcinoma), and smoking status (smoker vs non-smoker). The primary endpoint in the unblinded intention-to-treat analysis was 2-year disease-free survival. This ongoing study is registered with ClinicalTrials.gov , number NCT01683175. Findings Between Sept 8, 2012, and May 21, 2015, 102 patients from 16 centres across China were enrolled and randomly assigned to receive erlotinib (n=51) or chemotherapy (n=51). Median follow-up was 33.0 months (IQR 17-8-43-1). 2-year disease-free survival was 81.4% (95% CI 69.6-93.1) in the erlotinib group and 44.6% (26 -9-62- 4) in the chemotherapy group (relative risk 1.823 [95% CI 1.194-2.784; p=0.0054). The difference in 2-year disease-free survival between the groups was 36.7% (95% CI 15 - 5-58- 0; p=0.0007). Adverse events of any grade occurred in 29 (58%) of 50 patients in the erlotinib group and 28 (65%) of 43 patients in the chemotherapy group. Grade 3 or worse adverse events occurred in six (12%) of 50 patients in the erlotinib group versus 11 (26%) of 43 in the chemotherapy group; the most common of these in the erlotinib group was rash (in two 14%1 of 50 patients) and in the chemotherapy group were decreased neutrophil count (in seven [16%] of 43 patients) and myelosuppression (in four [9%]). No treatment-related deaths were reported. Interpretation Adjuvant erlotinib improved 2-year disease-free survival in patients with EGFR mutation-positive stage IIIA NSCLC compared with chemotherapy, with a better tolerability profile. This study suggests that tyrosine kinase inhibitors could have a potentially important role as adjuvant therapy in EGFR mutation-positive stage IIIA NSCLC. However, this trial was a phase 2 study. Mature overall survival data are also needed. Ongoing studies will hopefully confirm the role of adjuvant EGFR tyrosine kinase inhibitor therapy in patients with NSCLC. Copyright (C) 2018 Elsevier Ltd. All rights reserved.