Consensus on adjuvant therapy for completely resected non-small cell lung cancer until 2002 was as follows. (1) There was no significant impact of postoperative adjuvant chemotherapy based on meta-analysis and previous clinical trials. (2) Confirmatory studies are necessary in large-scale prospective clinical trials. However, recent mega trials have introduced epoch-making changes for postoperative adjuvant chemotherapy in clinical practice since ASCO 2003. The effectiveness of UFT in N0 patients was confirmed. Patients with completely resected stage I non-small cell lung cancer, especially T2N0 adenocarcinoma, will benefit from adjuvant chemotherapy with UFT. The results of the International Adjuvant Lung Trial (IALT) have confirmed the meta-analysis in 1995. Also, both the JBR10 and Cancer and Leukemia Group B (CALGB) 9633 studies have also confirmed positive IALT results of the benefit for postoperative platinum-based chemotherapy in completely resected non-small cell lung cancer. Adjuvant chemotherapy for pathological stage IB to II, completely resected non-small cell lung cancer is standard care based on clinical trials. UFT showed the strongest evidence for IB in Japan. Platinum doublet chemotherapy with third-generation anticancer agents is also recommended. Adjuvant chemotherapy should be offered as standard care to patients after completely resected early stage non-small cell lung cancer. However, there is no evidence of the feasibility and efficacy for adjuvant chemotherapy with the platinum-based regimen in Japan. Careful management should be necessary in such treatment.