The objective of this study was to explore the relationship between gefitinib exposure and clinical outcome in gefitinib-treated patients with advanced non-small cell lung cancer. Thirty patients participated in this pharmacokinetic study and received 250-mg oral doses of gefitinib once daily. Blood samples were collected before dosing and on days 7, 14, 21, and 28. The plasma concentrations of gefitinib were evaluated using a validated high-performance liquid chromatographic method with tandem mass spectrometric detection. Univariate and multivariate analyses were performed to determine predictive factors for response and survival of patients. EGFR mutations were analyzed retrospectively. Median survival time (MST) was 9.97 months (95%CI 2.79-17.14 months). The geometric mean trough gefitinib plasma concentration (Cminss was 266 ng/ml (range 94-538 ng/ml). In the multivariate analysis, only skin rash was associated with gefitinib-induced disease control (P=0.017); Adenocarcinoma, skin rash, and 'high' Cminss (Cminss≥200 ng/ml) were independently associated with overall survival (P=0.004, 0.028,0.007, respectively). MST of EGFR wild-type patients with 'high' Cminsswas longer than that with 'low' Cminss (P=0.002). Our study results show that pharmacokinetic variability may also account for the different outcomes following treatment with gefitinib for patients with wild-type EGFR. Further studies are needed to confirm these results.