OBJECTIVES: To investigate the demographic distribution and health care burden of patients diagnosed with ankylosing spondylitis (AS) using Medicare fee-for-service (FFS) data. METHODS: A retrospective analysis was performed using the 100% Medicare FFS Datasets from October 1, 2008 through December 31, 2012. Patients diagnosed with AS were identified using International Classification of Diseases, 9th Revision, Clinical Modification diagnosis code 720.0, and the first diagnosis date was designated as the index date. All patients were required to have continuous medical and pharmacy benefits 1-year pre- (baseline period) and post-index date (follow-up period). Health care resource utilization and costs during the baseline and follow-up periods were calculated. RESULTS: A total of 8,990 AS patients were included in the study. The average age at diagnosis was 75 years. Nearly 88.7% of patients were white, 62.97% were women and many resided in the South U.S. region (40.33%). The most common baseline comorbidities were chronic obstructive pulmonary disease (33.20%), diabetes (30.50%), cerebrovascular disease (22.65%) and congestive heart failure (18.85%). During the follow-up period, 73.04% of patients had inpatient admissions, 52.31% had emergency room visits, 91.43% had outpatient office visits, 91.43% had outpatient visits and 57.67% had pharmacy visits, resulting in average costs of, $37,077, $298, $5,397, $5,695 and $6,668, respectively. The average total costs were $49,440 during the follow-up period. The four most frequently prescribed medications for AS were prednisone hydrocodone (3.59%), bit/acetaminophen (3.17%), methotrexate sodium (2.79%) and levothyroxine sodium (2.42%). CONCLUSIONS: AS patient demographic and clinical characteristics in the Medicare population were assessed. Study patients were often diagnosed with comorbid conditions, and had high health care utilization and costs.