Study Design: Retrospective study of a posterior approach for surgical treatment of thoracolumbar pseudarthrosis in ankylosing spondylitis (AS). Objective: The aim of the current study was to report the surgical results of symptomatic thoracolumbar pseudarthrosis in AS through a posterior approach. Summary of Background Data: Spinal pseudarthrosis is a well-known complication in AS. The condition may complicate with mechanical back pain, spinal deformity, and sometimes neurological deficits. Conservative treatment often fails in this situation and surgical treatment is required. However, the optimal surgical procedure for this condition is still controversial. Methods: From January 2006 to December 2011, 12 AS patients with spinal pseudarthrosis at the thoracolumbar segment were treated surgically after failure of >3 months conservative treatment. The indications for surgery were persisting back pain in all patients, combined with neurological deficits in 4 patients and spinal deformities in 3 patients. Transforaminal or transpedicular debridement of the pseudarthrosis at the anterior column was performed from a posterior approach. After complete debridement, bone graft at the anterior open wedge defect of the pseudarthrosis was performed from a posterior approach. Posterior pedicle screws were placed for fixation. Clinical and radiographic outcomes were assessed with an average follow-up of 28 months (range, 24-36 mo). Results: The persistent back pain obtained significant relief in all cases after surgery. Four patients with neurological deficits showed complete recovery of neurological function at follow-up. The spinal deformities in 3 cases obtained correction. Solid bony fusion was achieved in all cases, and there was no correction loss at follow-up. Conclusions: In AS with symptomatic thoracolumbar pseudarthrosis, a posterior transforaminal or transpedicular approach can provide circumferential stability, anterior bone graft, and neurological decompression simultaneously. A supplemental anterior approach may be avoided by this method.