1. Annals of the Rheumatic Diseases Between 1948 and 1971, 533 patients with definite ankylosing spondylitis (AS) were present among approximately 25,000 patients attending (i.e. 2-5 per cent. compared with approximately 25 per cent. with rheumatoid arthritis). When these patients with AS were followed up, this partly prospective/retrospective study gave the following results: Sex incidence: Males;94 (18 1;Females; Ratio 4; per cent