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This is a retrospective clinical study.To investigate the correction angle and safety of the spinal osteotomy at the T12 or L1 vertebra.Monosegment subtraction osteotomy cannot effectively correct severe kyphosis in ankylosing spondylitis (AS), generally 2-level spinal osteotomy was taken for achieving expected correction. According to literature, the T12 or L1 were usually taken as the upper spinal osteotomy vertebra. Because of the canalis vertebralis at the T12 and L1 were spinal cord and medullary cone, so the spinal osteotomy at the T12 or L1 vertebra were more dangerous than at lower level. The correction angle and safety of the spinal osteotomy at the T12 or L1 vertebra have not yet been reported.From July 2009 to 2014, 33 patients in our department with severe AS kyphosis underwent 2-level pedicle subtraction osteotomy were studied. Preoperative and postoperative relevant parameters and complications were recorded.The upper spinal osteotomy was taken at the T12 vertebra for 10 patients. The upper spinal osteotomy was taken at the L1 vertebra for 23 patients. The mean amount of correction of T12 and L1 was 26.230 and 27.952 degrees, respectively. All patients could walk with orthophoria and lie horizontally postoperatively. No deadly vascular and neurological lesion occurred.Performing pedicle subtraction osteotomy at T12 and L1 can safely achieve a mean correction of 26.230 and 27.952 degrees, respectively. Two-level osteotomy was safely and advocated for correcting severe AS kyphosis.Level III.