Purpose <p>To investigate the influence of apical vertebrae difference (AVD) on surgical decision-making and clinical outcomes of single- and two-level osteotomy in ankylosing spondylitis (AS) thoracolumbar kyphoscoliosis with sagittal and coronal imbalance.</p> Methods <p>A total of 27 AS patients with thoracolumbar kyphoscoliosis were enrolled in the study. Patients were divided into single- and two-level osteotomy groups based on the number of osteotomy levels. Coronal, sagittal, and clinical parameters were measured preoperatively, postoperatively, and at the last follow-up. AVD, operation time, blood loss, fused segments and complications were recorded between the two groups.</p> Results <p>Among 27 patients, 11 underwent single-level osteotomy and 16 underwent two-level osteotomy. The operation time, blood loss and number of fused segments were lower in single-level group compared to the two-level group (<i>P</i> &lt; 0.001). Coronal, sagittal, and clinical parameters improved significantly after surgery (<i>P</i> &lt; 0.05), with only osteotomized vertebral angle (OVA) showing a significant difference between the two groups (<i>P</i> &lt; 0.05). The average AVD was 1.50 segments in single-level group and 3.30 segments in two-level group. Additionally, single- and two-level osteotomy accounted for 80% and 20% in group A, 77.8% and 22.2% in group B, and 0% and 100% in group C, respectively.</p> Conclusion <p>AVD was a crucial parameter in determining whether single- or two-level osteotomy was appropriate for AS patients with thoracolumbar kyphoscoliosis. If the AVD was &lt; 3 segments, single-level osteotomy should be considered. If the AVD was ≥ 3 segments, two-level osteotomy was recommended.</p>