The development of Burkitt’s lymphoma (BL) is uncommon in elderly people. Most treatment-related hematological malignancies are of a myeloid lineage. Only a few cases with BL secondary to cancer treatment have been described. We report a rare case of an elderly patient with radiotherapy-related BL. A 71-year-old Japanese man, who had a past history of oropharyngeal cancer treated with local irradiation 15 years ago, presented with a left mandibular mass in December 2004. A partial mandibulectomy disclosed pathological features consistent with BL. Although the patient was initially treated with intensive chemotherapy, the development of complications precluded further anticancer drug treatment. Rituximab was administered once weekly for 5 consecutive weeks, with resolution of the mandibular mass. He remained in remission without further lymphoma treatment for more than 3 years after diagnosis. Rituximab monotherapy should be considered as a therapeutic option for elderly patients with BL.