Twenty-two patients suffering from progressive kyphosis due to ankylosing spondylitis underwent one or more lumbar osteotomies during 1957-1983. The primary thoracic kyphosis was 80 degrees (45 degrees-155 degrees). The mean correction obtained by one level osteotomy was 44 degrees (30 degrees-60 degrees). The mean loss of correction after 3 years was 5 degrees. The use of internal fixation reduced the loss of correction from 9 degrees to 1 degree, also allowing ambulatory after-care and a shorter period of immobilization in plaster or jackets. We had no fatal and relatively few non-fatal complications; three cases of retrograde ejaculation were observed however. All the patients reported subjective respiratory improvement.