Criteria for use in population surveys to study the epidemiology of ankylosing spondylitis were proposed at the CIOMS Symposium in Rome in 1961, and a revised set of criteria were introduced at the next symposium in New York in 1966. The Rome criteria specify that the diagnosis of ankylosing spondylitis should be made when bilateral sacroiliitis and one offive clinical criteria are present, or when four clinical criteria are present. Using these criteria, therefore, it is possible to make a diagnosis of spondylitis without radiological evidence of disease. However, bilateral sacroiliitis is recognized as the most important criterion and has a weight three times greater than any of the clinical criteria. Recently, we have developed simple objective clinical methods to measure spinal mobility in each of the stipulated directions of movement-anterior flexion, lateral flexion, and extension. Furthermore, we have particularly emphasized the importance of allowing or the effects of age and sex not only on spinal mobility but also on chest expansion.