Nine radiodiagnostic rules are drawn from the X-rays of 2125 ankylosing spondylitis patients. The significance of early diagnosis of the 'multicolored' saroiliac X-ray is looked onto; the syndesmophyte, squaring-phenomenon, barrel-shaped vertebra, Romanus and Andersson lesions, and the ossification of ligaments are discussed. The changes at the apophyseal and the costovertebral joints, unimportant for early diagnosis, are explored.