The present case is a patient with advanced non-small cell lung cancer (NSCLC) who developed leukoencephalopathy following radiotherapy and gefitinib treatments.There are rarely reports of such incidences because the median survival period of advanced NSCLC is only ten months.The features of leukoencephalopathy in this case were atypical for radiation leukoencephalopathy,so it was suspected that the leukoencephalopathy was associated with gefitinib.