Radiation therapy for thoracic malignancies is often complicated by radiation-induced esophagitis. Symptoms of radiation esophagitis are nonspecific and include dysphagia, odynophagia, and chest pain. Patients receiving radiation therapy are also at risk for infectious esophagitis, which can be indistinguished clinically from radiation-induced esophagitis. We retrospectively reviewed data on patients who had esophagitis symptoms during or after thoracic radiation therapy and were referred for upper endoscopy. We sought to determine how often infectious esophagitis or cancer was present, as compared to radiation-induced esophagitis alone. Twenty-four upper endoscopies were performed on 16 patients over a three-year period to evaluate esophagitis symptoms. Forty-four percent of the patients endoscoped had infectious esophagitis or recurrent cancer diagnosed by endoscopy. No complications occurred from the procedures. Esophagoscopy is a safe procedure that should be considered, to exclude infection or cancer, in patients who develop esophagitis symptoms during or after thoracic radiation.