Background: The optimal timing of treatment with EGFR-tyrosine kinase inhibitors (EGFR-TKI) in NSCLC patients has not yet been determined. Methods: We separated 228 patients with advanced /metastatic NSCLC treated with gefitinib into an early gefitinib group (patients who received gefitinib as first- or second-line treatment) and a delayed gefitinib group (patients who received gefitinib as third or fourth-line treatment) and attempted to determine whether the timing of gefitinib treatment affected clinical outcomes. Results: Median overall survival (OS), progression free survival (PFS), and median OS from first-line treatment of advanced/metastatic disease (OSt) for 111 patients in the early gefitinib group were 6.2 months, 3.3 months, and 11.6 months. However, median OS, PFS, and OSt for 84 patients in the delayed gefitinib group were 7.8 months, 2.3 months, and 22.7 months. No differences in OS and PFS were observed between the 2 groups. However, OSt was significantly longer in the delayed gefitnib group. Timing of gefitinib therapy was one of the independent predictors of OSt. Hb ${geq}$ 10 g/dl, and having never smoked, and ECOG performance status ${leq}1$ were independent predictors of better PFS. Conclusion：Deferral of gefitinib therapy in patientswith advanced ormetastatic NSCLC may be preferable if they are able to tolerate chemotherapy.