We performed esophageal endoscopy with concurrent chemo-radiotherapy for lung cancer in 19 patients. Endoscopical examination proved that seven patients (36.8%) had esophageal erosion or coating (grade 2), four patients (21.1%) had ulcer or bleeding (grade 3) confined to the radiation field, and only one patient (5.3%) had severe symptoms (WHO grade 3). There was a discrepancy between patients' symptoms and endoscopical findings. Endoscopically proven esophagitis, that is, erosion or coating (grade 2), and ulcer or bleeding (grade 3), was more frequent in the daily low-dose chemotherapy group (5/5) than in the full dose chemotherapy group (5/14) (p < 0.05). One patient with grade 3 endoscopial damage showed less recovery in spite of three months medication. In concurrent radiochemotherapy in which the radiation field includes the esophagus, careful attention should be given to radiation esophagitis, which may be underestimated when assessed on the basis of subjective symptoms alone. Therefore, endoscopy is recommended even if patients have few complaints, and once the esophageal ulcer is proven (grade 3), it should be closely followed up using endoscopy.