Gefitinib is an orally active epidermal growth factor receptor tyrosine kinase inhibitor, and it shows favorable antitumor activity against chemorefractory nonsmall cell lung cancer (NSCLC). However, patients with NSCLC have few treatment options available if they are refractory to gefitinib. We describe a 49-year-old patient with NSCLC who had a complete response to initial gefitinib that lasted for 12 months. The tumor relapsed, and the patient received cytotoxic chemotherapy. However, despite chemotherapy, the patient had radiographic progression of lung metastases and we commenced retreatment with gefitinib, showing a remarkable effect. Epidermal growth factor receptor (EGFR) gene analysis showed deletion mutations in codon 745-750 in exon 19 and EGFR gene amplification. Our case shows that after retreatment with gefitinib, patients may show a remarkable response if they showed a remarkable response to initial gefitinib administration and if a certain time has elapsed since the previous gefitinib treatment.