Background: The role of HLA-B27 in rheumatic disease is reviewed.

Methods: The PubMed database was searched for the code words HLA-B27, ankylosing spondylitis, or their combinations. The diagnostic value of HLA-B27 for ankylosing spondylitis was calculated using Bayes' theorem.

Results: It is still not clear whether HLA-B27 is a contributing causal factor for ankylosing spondylitis and reactive arthritis. Knowledge of a patient's HLA-B27 status for establishing prognostic information is of uncertain clinical value.

Conclusions: Knowledge of HLA-B27 status has limited diagnostic value. HLA-B27 status is clinically most informative when the test result is negative, as ankylosing spondylitis can be ruled out.