Ankylosing spondylitis (AS) is a systemic inflammatory disease that can result in chronic pain and disability. This study aimed to analyse the prevalence and risk of medical comorbidities in patients with AS compared with the general population. 11 701 patients with AS and 58 505 matching controls were selected for analysis from the National Health Insurance Research Dataset (NHIRD) in Taiwan. The Elixhauser comorbidity index was used for selecting medical comorbidities. Pearson chi2 tests and conditional logistic regression a nalyses were performed to examine the prevalence and risk of comorbidities between these two groups. Patients with AS were at increased risk for multiple systemic comorbidities including cardiovascular, neurological, pulmonary, gastrointestinal, endocrine, haematological and mental illness. The most prevalent comorbidities in patients with AS were hypertension (16.4%), peptic ulcers (13.9%) and headaches (10.2%). The results show that patients with AS have a higher prevalence of multiple comorbidities than the general population in Taiwan. These findings are consistent with previous studies done in Western populations. The results could be useful for both the clinical management of patients with AS and for researching the underlying pathological mechanisms.