Study Design, A retrospective study was done in 12 teenagers with severe L5-S1 spondylolisthesis surgically treated with a single-stage posterior procedure for reduction, posterior interbody fusion, and segmental instrumentation. Objective. To evaluate the effectiveness and reliability of intraoperative reduction and posterior interbody fusion in severe lumbosacral spondylolisthesis in children. Summary of Background Data. Twelve young patients (age, 13-18 years; mean = 16 +/- 1.5) with severe L5-S1 spondylolisthesis (slip, 59%-85%; mean = 70.4 +/- 8.8%) were available for follow-up evaluation (6-24 months after surgery). All presented with serious preoperative clinical signs (tight hamstrings, waddling gait, lumbosacral pain, radiated leg pain). Methods, The patients underwent surgery using a single posterior surgical procedure. After removal of the loosened arch and complete discectomy, a temporary device placed bilaterally between L1 and the sacral wings was used to achieve reduction by distraction. This was followed by a posterior interbody strut graft and pedicle segmental fixation. No postoperative casting was used. Clinical examination was done, and radiographic measurements were taken after surgery and at follow-up evaluation. Patients were evaluated for fusion rate, stability of reduction, clinical outcome, and possible complications. Results, All patients underwent solid fusion without loss of reduction. No intraoperative or postoperative complications were observed. Mean correction of the initial slipping was 79.5 +/- 7% of the initial deformity. No clinical signs were present at follow-up evaluation. Conclusions. Intraoperative distraction appears to be truly effective in reducing severe lumbosacral olyshtesis in children. Posterior interbody fusion (and eventual sacral dome osteotomy) successfully combines the goals of solid fusion with the requirements of root decompression, Mo neurologic problems were seen as a consequence of distraction. The solidity of the posterior segmental pedicle instrumentation combined with the anterior strut graft eliminate the need for postoperative casting.