A 70-year-old woman with rheumatoid arthritis treated with methotrexate (MTX) complained of right arm weakness. On CT and MRI, tumors were found in the right frontal lobe, bilateral lungs, and left renal parenchyma. She was diagnosed as having lymphomatoid granulomatosis (LYG) grade 2 on thoracoscopic biopsy of the left lung. We discontinued MTX and treated a mass lesion in the right frontal lobe with stereotactic radiotherapy. As a result, the tumors showed a gradual reduction in size, and the patient achieved complete remission. LYG is a rare lymphoproliferative disorder, and has various clinical characteristics. We describe herein a patient with LYG grade 2 with cerebral, pulmonary, and renal lesions, who has maintained a complete remission for six months, to date, after treatment.