We describe a 54-year-old female patient with rheumatoid arthritis (RA) and Sjögren's syndrome (SS) who presented with right chest pain and a large mass visible in the upper right field of a chest X-ray. Computed tomography (CT) showed multiple tumours in both lungs, the liver, and the spleen. The right lung tumour was 8 cm in diameter with a cavity. Biopsy of the lung and liver revealed lymphomatoid granulomatosis (LG) and diffuse large B-cell lymphoma (DLBCL). These lesions spontaneously regressed after withdrawal of methotrexate without any therapy for the lymphoma. This is the first report of self-limiting LG in a patient, complicated with methotrexate-treated RA.