The prevalence of ankylosing hyperostosis in a Jewish hospital population is presented. In individuals over the age of 40 years the overall prevalence was 22.4% in males and 13.4% in females. The prevalence increased with age to a maximum of 46% in males and 30% in females over the age of 80 years. A method of grading the disease according to extent is described. The most extensive grade III is seen almost exclusively in males.