Despite numerous attempts to uncover the mechanism of other iatrogenic immunodeficiency-associated lymphoproliferative diseases (OIIA-LPDs), this mechanism remains poorly understood, especially in rheumatoid arthritis (RA) patients. We analyzed the data on 23 patients with LPDs and RA. Patients were categorized into three groups according to whether they had methotrexate (MTX); MTX-regressive LPDs, MTX-persistent LPDs or other drugs-mediated LPDs. The LPDs seen in OIIA-LPDs-RA might have a unique behavior to think about several rare phenotypes. The overall survival of all patients was 74% at 5 years, and those of the three groups were 100%, 64% and 60%, respectively. Among the 6 patients who died, 4 had LPDs that were detected late, and thus adequate treatment was not given. In addition, several patients with diffuse large B cell lymphoma with a complex karyotype achieved complete remission (CR). Only one among the 17 patients who achieved CR relapsed. OIIA-LPDs-RA appeared to have a better prognosis than other more common types of lymphomas. Regarding RA treatment, various anti-RA drugs were given to the patients after developing LPDs, including MTX, but no recurrent patients were documented.