The purposes of this study are to investigate medical resource utilization and medical costs of Korean rheumatoid arthritis (RA) patients and to analyze predictors in relation to medical costs. National claims data on medical treatment were analyzed for the 151,472 RA patients in 2009. For outpatients, the mean annual number of visits was 32.5, and the mean annual total outpatient care costs were 2.0 million KRW (US$1,594) per patient. On the other hand, the mean annual length of stay of inpatients was 22.2 days, and the mean annual total inpatient care costs were 3.8 million KRW (US$3,013). Average annual total medical costs per patient for all of the RA patients were 2.9 million KRW (US$2,310). Total medical costs consisted of 26.1% outpatients' costs, 25.4% inpatient, and 48.6% medication costs, making medication costs a predominant cost driver. In the multiple regression analysis, biologic use was an important cost factor in relation to the annual total medical costs. This study provides information on the cost of illness of RA with the population-based representative RA patients in Korea, which had not been reported until now.