OBJECTIVES: Rheumatoid arthritis (RA) is among the most common rheumatic diseases in Japan. There are no large studies of costs of care of RA in Japan. We report results from the first and only large, long-term outcome study of RA in Japan. METHODS: J-ARAMIS is a prospective non-interventional observational cohort study of consecutively enrolled patients with rheumatoid arthritis seen at the Institute of Rheumatology in Tokyo. Physician and patient self-report data on outcomes, medication use, adverse events and satisfaction with care is collected using the validated J-HAQ. Outpatient costs of care are calculated from billing records of IOR. Costs for hospitalizations are estimated by using a per-day cost of JPY 20,970 (based on “Survey of Medical Care Activities Public Health Insurances", Ministry of Health, Labor and Welfare, Japan, 2000). RESULTS: The J-ARAMIS program has averaged patient response rates of over 98% to date. A total of 5,666 patients have been enrolled, with a total observation time of 8489.5 patients-years. The average age is 56.4 years (SEM 0.17), with mean disease duration of 9.6 years (SEM 0.12). The mean Body Mass Index is 21.5 (SEM 0.07) and the average disability index is 0.75 (SEM 0.01), both significantly below the numbers seen in the Western countries. The average direct cost of medical care in RA patients is JPY 417,134 per year (SEM JPY 32040). Medications account for 55.4% of these costs, with laboratory and radiology investigations accounting for 22.5%, hospitalizations 13.9%, physician visits 7.2% and rehabilitation 1%. CONCLUSIONS: The medical costs of care of RA patients in Japan are similar to the previously published estimates from the US, but the distribution of costs is significantly different from that seen in the US. RA patients in Japan also have lower levels of disability compared to patients with similar levels of disease duration in the US.