A study of patients with advanced non-squamous non-small cell lung cancer (NSCLC) evaluated epidermal growth factor receptor (EGFR) mutation status and serum hepatocyte growth factor (HGF) for their associations with response to gefitinib therapy and prognostic impact. An enzyme-linked immunosorbent assay was used to determine levels of HGF in serum from 96 Japanese patients with advanced non-squamous NSCLC. The peptic nucleic acid-locked nucleic acid clamp method was used to determine their EGFR somatic mutation status. We evaluated the relationship between each independent clinicopathological variable and the response to gefitinib therapy and risk factors associated with prognosis. HGF-positive serum status (hazard ratio, 1.536; 95% confidence interval, 1.042-2.400; P = 0.0295) had a significant and independent negative effect on progression-free survival among patients with wild-type EGFR. We demonstrate that having HGF-positive serum is predictive of a negative response to gefitinib therapy in patients with advanced NSCLC who harbor wild-type EGFR.