Information-theoretical considerations demonstrate the uselessness, in terms of understanding and diagnosis, of seven different systems for grading sacroiliitis in ankylosing spondylitis used by German, French, Canadian, Norwegian, Swedish, and Swiss authors. The illustrations prove that it is not possible to differentiate between a normal and abnormal (inflammatory) x-ray of the sacroiliac joints without the application of tomography. A grading system promises diagnostic and communicative success only when based upon tomography results (6 standard sections in adults), and when it takes the "multicolored picture" into consideration ("multicolored picture": no = sacroiliitis stage 0; yes = stage 1; complete bilateral ankylosis: yes = stage 2).