The epidemiology of ankylosing spondylitis.

This review focuses on various epidemiological aspects of ankylosing spondylitis (AS). Diagnostic criteria currently available are described, and their use in scientific studies as opposed to everyday clinical practice is discussed. Present knowledge of the prevalence of AS is addressed in detail with particular emphasis on discrepancies caused by variations in population frequencies of HLA B27 and those caused by differences in study designs.