A 74-year-old woman was admitted to a local hospital for investigation of a rapidly growing mass in her neck, and exertional dyspnea. An open biopsy confirmed a diagnosis of non-Hodgkin's lymphoma of the thyroid (NHLT), of a diffuse large cell type. The patient was referred to our department for radio-chemotherapy for stage I E NHLT. She was given radiotherapy in the form of 40 Gy radiation directed at her neck and superior mediastinum, with one course of chemotherapy using cyclophosphamide, adriamycin, vincristine, and prednisolone (CHOP). After radio-chemotherapy, the tumor was obviously smaller. Because the patient refused further chemotherapy, she underwent salvage surgery, after being sufficiently advised, and with her informed consent. Histological examination of the removed thyroid tissue showed that the radio-chemotherapy had produced a complete response. Thus, we believe that an open biopsy should be performed early to confirm the diagnosis of lymphoma histologically and to determine the degree of malignancy. We also stress the fact that NHLT is presently most effectively treated by radiotherapy combined with several courses of CHOP chemotherapy. The role of surgery in the treatment of NHLT is diminishing.