The objective of the study is to describe the use, clinical efficacy, and toxicity of nonsteroidal anti-inflammatory drug (NSAID) therapy in patients with ankylosing spondylitis (AS). A cross-sectional population study of 1,080 AS patients was carried out by a written questionnaire in the year 2000. Seventy-eight percent of AS patients had regularly taken NSAIDs for their disease 12 months prior to the study. Most AS patients commonly used diclofenac, naproxen and indomethacin. AS patients were generally rather satisfied with the efficacy of their therapy where 19.1% reported complete pain control, 26.8% reported pain reduction to one quarter, and a further 34.4% reported pain reduction to one half. However, over 20% of patients taking NSAIDs still reported insufficient pain control and more than 40% changed the NSAID due to lack of efficacy. One quarter of AS patients reported severe side effects from their treatment, most commonly abdominal pain, headache and dizziness, and nausea. There was no effect on age or duration of disease on the occurrence of NSAID-related side effects. Medications were commonly ceased or changed due to inefficacy or side effects. The percentage of AS patients reporting changing their NSAID due to side effects ranged from 10.5% for celecoxib to 31.4% for indomethacin. We conclude that NSAIDs are effective in the management of inflammatory symptoms of many, but not all, patients with AS. There is a significant side effect profile, which frequently results in medication change or cessation. Anti-tumor necrosis factor therapy may reduce the need for intensive long-term NSAID therapy in AS.