To evaluate the efficacy of pemetrexed plus cisplatin versus vinorelbine plus cisplatin as postoperative adjuvant chemotherapy in patients with pathologic stage II-IIIA nonsquamous non-small-cell lung cancer (NSCLC).We performed a randomized, open-label, phase III study at 50 institutions within 7 clinical study groups in Japan. Patients with completely resected pathologic stage II-IIIA (TNM 7th edition) nonsquamous NSCLC were randomly assigned to receive either pemetrexed (500 mg/m2, day 1) plus cisplatin (75 mg/m2, day 1) or vinorelbine (25 mg/m2, days 1 and 8) plus cisplatin (80 mg/m2, day 1) with stratification by sex, age, pathologic stage, EGFR mutation, and institution. These treatments were planned to be given every 3 weeks for 4 cycles. The primary end point was recurrence-free survival in the modified intent-to-treat population, excluding ineligible patients.Between March 2012 and August 2016, 804 patients were enrolled (402 assigned to vinorelbine plus cisplatin and 402 assigned to pemetrexed plus cisplatin). Of 784 eligible patients, 410 (52%) had stage IIIA disease and 192 (24%) had EGFR-sensitive mutations. At a median follow-up of 45.2 months, median recurrence-free survival was 37.3 months for vinorelbine plus cisplatin and 38.9 months for pemetrexed plus cisplatin, with a hazard ratio of 0.98 (95% CI, 0.81 to 1.20; 1-sided P = .474). Grade 3-4 toxicities reported more frequently for vinorelbine plus cisplatin than for pemetrexed plus cisplatin were febrile neutropenia (11.6% v 0.3%, respectively), neutropenia (81.1% v 22.7%, respectively), and anemia (9.3% v 2.8%, respectively). One treatment-related death occurred in each arm.Although this study failed to show the superiority of pemetrexed plus cisplatin for patients with resected nonsquamous NSCLC, this regimen showed a better tolerability as adjuvant chemotherapy.