From 1990 to 1993 we treated 22 consecutive patients who had progressive spinal kyphosis due to ankylosing spondylitis by a closing-wedge posterior vertebral osteotomy with partial corporectomy of L4 and transpedicular fixation. The average correction was 32 degrees (24 to 52) with a mean loss of correction after operation of 2.7 degrees (0 to 13). The average operating time was 185 minutes (135 to 240) and blood loss was 2500 ml (1200 to 5000). The osteotomy corrected all patients sufficiently to allow them to see ahead and their posture was improved. There were no fatal complications, but in two cases there was failure of the instrumentation and one patient needed reoperation for nerve compression. Two deep wound infections required removal of the implant and six patients had superficial skin infections under the plaster. The use of a circoelectric bed and intermittent prone lying eliminated this problem.