Chemotherapy and radiotherapy were performed on patients over 70 years of age with malignant lymphoma of the thyroid gland and complete remission (CR) was achieved in three patients who are reported here. Case 1: An 87-year-old woman who had been treated for Hashimoto's disease for 10 years as an outpatient was diagnosed as having a diffuse-small cell, B-cell type lymphoma by an aspiration biopsy of the tumor in the left thyroid. COP-BLAM chemotherapy followed by radiotherapy achieved CR. Case 2: A 71-year-old woman was referred to our department because of a right cervical tumor. A biopsy of the tumor revealed a diffuse medium-sized, B-cell type lymphoma. She also has been proved to have hypothyroidism. She entered CR after COP-BLAM chemotherapy combined with a radiotherapy. Case 3: A 76-year-old male patients with Hashimoto's disease who had been treated for 12 years at another outpatient clinic, presented with a right cervical tumor. Aspiration biopsy of the tumor yielded a diagnosis of B-cell lymphoma. COP-BLAM chemotherapy combined with radiotherapy achieved a CR. All three patients entered CR after chemotherapy combined with radiotherapy. Moreover, the microsome test and thyroid test also became negative after the combined modality therapy. In the future, there will probably be increases in the incidence of malignant lymphoma of the thyroid gland, due to the aging of society, and it will be necessary to establish methods of diagnosis and treatment for this disease.