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A prospective study was performed in 45 patients with ankylosing spondylitis.To assess the outcomes of decancellation pedicle subtraction extension osteotomy in ankylosing spondylitis patients with severe fixed kyphotic deformity.There have been several studies regarding correction of kyphotic deformity in ankylosing spondylitis. However, most of them concern surgical technique. There have been no reports concerning clinical results of decancellation pedicle subtraction osteotomy in ankylosing spondylitis.The kyphotic deformity was corrected by a one-stage pedicle subtraction extension osteotomy. Radiographic assessment for sagittal balance was performed by measuring thoracic kyphosis, lumbar lordosis, distance between the vertical line on anterosuperior point of T1 and that of S1, and sacral inclination. Chin brow–vertical angle was measured on the preoperative and postoperative clinical photograph of patients. Clinical outcomes were assessed by questionnaire measuring changes in physical function, indoor activity, outdoor activity, psychosocial activity, pain, and patient satisfaction with surgery.Final follow-up radiograph showed an increase in lumbar lordosis from 10° to 44° (an increase of 34°), whereas thoracic kyphosis remained stable from 50° to 54°. Sagittal imbalance significantly improved from 94 to 8 mm, whereas sacral inclination increased from 8° to 24°. The chin brow–vertical angle was 32.0° before surgery and 0.9° after surgery. Satisfactory clinical outcome was achieved; however, clinical improvements did not correlate with changes in radiologic measurements.Most of the patients maintained good correction and had good clinical results. Based on the results of this study, pedicle subtraction extension osteotomy is effective for correction of kyphotic deformity in ankylosing spondylitis.