Irradical (R1-2) resection for non-small cell lung cancer (NSCLC) is associated with a dismal prognosis. Adjuvant treatment attempts to improve survival outcomes, but evidence on the optimal strategy is limited. The purpose of this study was to compare overall survival (OS) between different adjuvant treatment strategies in these patients.Out of 8,528 patients with newly diagnosed NSCLC from 2015-2018, those with an R1-2 resection were identified from the Netherlands Cancer Registry. First, OS was compared between adjuvant treatment groups ‘no therapy’, ‘radiotherapy (RT) only’, ‘chemotherapy only’, and ‘chemo- and radiotherapy (CRT)’ using multinomial propensity score-weighted Cox regression analysis. Second, three 1:1 propensity score-matched sets were created for chemotherapy vs no chemotherapy, RT only vs no therapy, and CRT vs chemotherapy only. Kaplan-Meier and Cox regression analyses for OS were performed in each set.With a median follow-up of 23 months, 427 patients were selected. In the weighted regression analysis, compared to no adjuvant therapy, chemotherapy and CRT were associated with improved OS (HR 0.41, 95%CI: 0.22-0.76; and HR 0.55, 95%CI: 0.37-0.81, respectively), whereas RT was not (HR 1.04, 95%CI: 0.73-1.50). In the matched sets, OS was improved after chemotherapy (+/- RT) compared to no chemotherapy (HR 0.47, 95%CI: 0.32-0.69). No OS difference was observed between matched groups of RT only vs no adjuvant therapy (HR 1.13, 95%CI: 0.74-1.72), nor for CRT vs chemotherapy only (HR 1.37, 95%CI: 0.70-2.71). Adjuvant chemotherapy, but not radiotherapy, improves survival after an R1-2 resection in stage I-III NSCLC.