The association of rheumatoid arthritis (RA) and immune thrombocytopenic purpura 
(ITP) has been reported rarely. Methotrexate, which is used for RA treatment, 
causes thrombocytopenia. Therefore, in medical practice, physicians avoid using 
methotrexate for RA in patients who have both RA and ITP. Here, we report an RA 
case that also had ITP, which did not decrease in platelet count after 
methotrexate therapy. A 50-year-old woman was diagnosed with diabetes mellitus 
in 1990, RA in 1995, and ITP in 2000. She had received hydroxychloroquine for 
more than 5 years. She was treated with prednisolone 16 mg/daily between 2006 
and 2007, but she discontinued this therapy because of weight gain. Laboratory 
findings were not remarkable, except for thrombocytopenia. We started 
methotrexate therapy 10 mg per week for treatment of RA, and hydroxychloroquine 
therapy was stopped due to nonresponse. The methotrexate dose was increased up 
to 15 mg/week. Her complete blood cell count was monitored frequently. We did 
not observe any decrease in platelet count, while active arthritis symptoms of 
the patient were relieved. This case shows that methotrexate may be used in 
patients diagnosed with RA that is associated with ITP under strict monitoring.