Objective: To analyze the outcomes of patients who received TKI immediately after the first-line without progression as maintenance treatment (immediate group) vs. those received delayed treatment upon disease progression as second-line therapy (delayed group). Methods: The study included 159 no-small-cell lung cancer (NSCLC) patients who received gefitinib or erlotinib as maintenance treatment in the immediate group (85 patients) or as second-line therapy in the delayed group (74patients). The primary end point was progression-free survival (PFS). EGFR mutation status was detected using denaturing high-performance liquid chromatography (DHPLC). Results: PFS was 17.3 and 16.4 months in the immediate and delayed groups, respectively (hazard ratio [HR],0.99; 95％ Confidence Interval [Cl]: 0.69-1.42; P=0.947). In a subgroup analysis that included only patients with EGFR mutation, however, PFS was significantly longer in the immediate group than in the delayed group (HR, 0.48; 95％ Cl:0.27-0.85; P=0.012). In patients with wild type EGFR, the risk for disease progression was comparable between the two groups (HR, 1.23; 95％ Cl: 0.61-2.51; P=0.564). No significant difference was demonstrated between the immediate and delayed group in terms of the overall survival (OS) (26.1 months vs. 21.6 months, respectively;HR=0.53; 95％ Cl: 0.27 to 1.06; P=0.072). There was also no difference in the incidence of adverse events between the two groups. Conclusions: EGFR TKI maintenance improves PFS in patients with EGFR mutation. Prospectively designed clinical studies that compare TKI immediate vs. delayed treatment after first-line chemotherapy upon disease progression are needed.