The aim of the present study was to assess ankylosing spondylitis (AS) patients' level of knowledge, using a self-administered multiple-choice questionnaire. The questionnaire, based on the Arthritis and Rheumatism Council (ARC) leaflet on AS, examined four areas: (A) general knowledge; (B) immunogenetic tests and inheritance; (C) general management; (D) joint protection, pacing and priorities. Statistical analysis was used to validate the questionnaire and to examine correlations with gender, age, disease duration and level of general education. The questionnaire was consistent, reliable and easy to read. The results showed AS patients to have a high level of knowledge (mean = 19.4, maximum possible = 25), although some wrong beliefs about the role of blood tests, the HLA-B27 antigen and inheritance were discovered. No statistical correlation was found between gender, age, duration of the disease, level of general education and the level of knowledge. These data suggest that this questionnaire is a simple way to detect the level of knowledge of patients with AS. The average score achieved by AS patients was outstanding, possibly reflecting the good quality of previous educational programmes. Patients' confusion regarding blood tests, genetics and inheritance was highlighted and should be addressed.