Most patients with non-small-cell lung cancer (NSCLC) present with advanced disease and have poor long-term prognosis. Gefitinib, a targeted therapy that prevents ATP binding in the tyrosine kinase domain of the EGF receptor, has been subject to comprehensive clinical development. A Phase III trial has demonstrated that gefitinib is superior to carboplatin/paclitaxel in terms of progression-free survival and objective response rate, as first-line treatment for pulmonary adenocarcinoma among never-smokers or former light smokers in East Asia (the IRESSA Pan-Asia Study), with the presence of an EGFR mutation being a strong predictor of the effect of gefitinib compared with carboplatin/paclitaxel. In this article, these results are discussed in the context of other recently reported studies of EGFR mutation-positive patients in both Asian and non-Asian countries. Furthermore, the clinical implications and future challenges for gefitinib are highlighted.