Between 1984 and 1993 we treated 21 consecutive patients who had progressive thoracic kyphosis due to ankylosing spondylitis by polysegmental posterior lumbar wedge osteotomies. In 19 patients we used the Universal Spinal Instrumentation System and in the last 2 patients the H-frame. The average correction in 20 of 21 patients at follow-up was 25.6 degrees (range 0 degrees-52 degrees), with a mean segmental correction of 9.5 degrees and a mean loss of correction after operation of 10.7 degrees (range 0 degrees-36 degrees). There were no fatal complications, but in one patient no correction could be obtained during surgery and another patient was reoperated due to lack of correction. Breaking out of screws through the pedicle during compressive correction was seen in seven patients. Implant failure, such as breakage of the threaded rods and/or loosening of the junction between the pedicle screw and the rod, occurred in 9 out of 21 patients. Two patients required reoperation at long-term follow-up. Five out of seven deep wound infections required removal of the implant. Polysegmental lumbar wedge osteotomies for correction of progressive thoracic kyphosis in ankylosing spondylitis is only recommended in patients at a mild stage of the disease with mobile discs and in combination with strong instrumentation.