A questionnaire drafted by the president of a self help group of patients suffering from ankylosing spondylitis (AS), the Danish Ankylosing Spondylitis Society (DASS), was completed by 179 of 184 (97%) consecutive patients with AS. The following results were found. The diagnosis of AS was delayed an average of 12.6 years for women and 9.5 years for men. No differences were found in age at onset of the disease. A comparison of juvenile and adult onset showed a higher incidence of initial peripheral articular manifestations in patients with juvenile ankylosing spondylitis. Stiffness progressed significantly in both sexes during the illness. Two men still had stiffness localised only to the lumbar spine after more than 20 years of illness. Twenty four of 47 women (51%) and 36/121 (30%) of the men had experienced extra-articular disease. Fifteen of 46 women (33%) and 18/121 (15%) of the men had iritis and conjunctivitis before the diagnosis of AS was established and later, in the course of the illness. The results of this study agreed with those of previous investigations. The advantage of using a questionnaire as a screening test is that many patients may be studied and information brought up to date in a simple and inexpensive way.