OBJECTIVES:To estimate and compare cost-of-illness (COI) and health-related quality of life (HRQOL) of rheumatoid arthritis (RA) and ankylosing spondylitis (AS) in South Korea. METHODS: Patients with RA (nϭ196) and AS (nϭ191) were surveyed by face-to-face interviews at the Rheumatology Clinic of Seoul National University Hospital. Direct costs [medical costs (treatment, drug, private physiotherapy, traditional Chinese medicine, other alternative medicine), non-medical costs (travel, dietary supplements, auxiliary device, home assistance)], indirect costs (productivity loss due to job loss and sick leave) and deterioration in HRQOL of RA and AS patients were measured. HRQOL was assessed using KEQ-5D. Factors associated with COI and HRQOL were analyzed using multiple regression and multivariate logistic regression. RESULTS