STUDY DESIGN: A prospective study on clinical, radiographic, and health-related quality of life (HRQoL) outcomes in children with acute spondylolysis treated with a rigid thoracolumbar orthosis or with an elastic lumbar support. OBJECTIVE: To compare outcomes of pediatric spondylosysis treated with a hard brace or an elastic lumbar support. SUMMARY OF BACKGROUND DATA: The benefits of the use of a rigid orthosis in treatment of spondylolysis are not clear. MATERIALS AND METHODS: Fifty-seven consecutive children with acute spondylolysis (mean age: 14.1 yr, range: 9-17 yr) were prospectively enrolled. Patients were treated with a rigid thoracolumbar orthosis (Boston brace) or with a low-profile, elastic lumbar support. First 14 patients were randomized the remaining 43 chose brace type themselves. Treatment period was four months. Treatment outcomes included bony union of the spondylolysis assessed with a computed tomography at four months and HRQoL using the Scoliosis Research Society-24 outcome questionnaire filled out before and after the treatment. RESULTS: Of the 57 patients, 54 completed the treatment protocol. Twenty-nine patients were treated using the Boston brace and 25 patients the elastic lumbar support. Bony union was obtained in 69.0% (20/29) of the Boston brace and in 60.0% (15/25) of the elastic lumbar support group patients. Difference in union rates was not significant (relative risk=1.14, 95% confidence interval: 0.44-2.98, P =0.785). There was no difference in the Scoliosis Research Society-24 total or domain scores at the end of follow-up between the treatment groups ( P >0.159 for all comparisons). In the whole cohort, the bony union did not predict better HRQoL in the end of the treatment ( P =0.869), although the pain domain improved significantly in the whole cohort ( P <0.001). CONCLUSIONS: A rigid thoracolumbar orthosis did not provide any benefits over an elastic lumbar support in terms of bony union or HRQoL outcomes in children with acute spondylolysis. LEVEL OF EVIDEN: 2.