The objectives of this study were to estimate the cost-of-illness (COI) and health-related quality of life (HRQOL) in patients with ankylosing spondylitis (AS) in Korea and to evaluate the effects of socio-demographic and clinical factors on the COI and the HRQOL. Face-to-face interview surveys were taken from patients with AS at the Rheumatology Clinic of Seoul National University Hospital. Direct medical and non-medical costs, indirect costs (productivity loss due to job loss and sick leave), and deterioration of HRQOL in patients with AS were measured. Factors associated with COI and HRQOL were analyzed with multiple regression and multivariate logistic regression. A total of 191 patients with AS was enrolled in the study. The COI in patients with AS amounted to 11,646,180 Korean Won (KRW) per patient, and their HRQOL was 0.62. As functional severity worsened, the total costs increased (class I, KRW 7.7 million; class II, KRW 12.9 million; classes III & IV, KRW 25.2 million) and the HRQOL scores decreased (class I, 0.72; class II, 0.61; classes III & IV, 0.24). Functional severity is the major determinant of the COI and HRQOL in patients with AS.