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Background: Thoracic anterior vertebral body tethering (TAVBT) is an emerging treatment for adolescent idiopathic scoliosis. Tether breakage is a known complication of TAVBT with incompletely known incidence. We aim to define the incidence of tether breakage in patients with adolescent idiopathic scoliosis who undergo TAVBT. The incidence of tether breakage in TAVBT is hypothesized to be high and increase with time postoperatively., Methods: All patients with right-sided, thoracic curves who underwent TAVBT with at least 2 and up to 3 years of radiographic follow-up were included. Tether breakage between 2 vertebrae was defined a priori as any increase in adjacent screw angle >5 degrees from the minimum over the follow-up period. The presence and timing of tether breakage were noted for each patient. A Kaplan-Meier survival analysis was performed to calculate expected tether breakage up to 36 months. χ 2 analysis was performed to examine the relationship between tether breakage and reoperations. Independent t test was used to compare the average final Cobb angle between cohorts., Results: In total, 208 patients from 10 centers were included in our review. Radiographically identified tether breakage occurred in 75 patients (36%). The initial break occurred at or beyond 24 months in 66 patients (88%). Kaplan-Meier survival analysis estimated the cumulative rate of expected tether breakage to be 19% at 24 months, increasing to 50% at 36 months. Twenty-one patients (28%) with a radiographically identified tether breakage went on to require reoperation, with 9 patients (12%) requiring conversion to posterior spinal fusion. Patients with a radiographically identified tether breakage went on to require conversion to posterior spinal fusion more often than those patients without identified tether breakage (12% vs. 2%; P =0.004). The average major coronal curve angle at final follow-up was significantly larger for patients with radiographically identified tether breakage than for those without tether breakage (31 deg±12 deg vs. 26 deg±12 deg; P =0.002)., Conclusions: The incidence of tether breakage in TAVBT is high, and it is expected to occur in 50% of patients by 36 months postoperatively., Level of Evidence: Level IV., Competing Interests: Compliance with Ethical Standards: (i) This study was given Ethical Approval by the Institutional Review Board prior to the conduct of this study. (ii) Informed consent was obtained from all participants. (iii) The authors received no funding for the preparation of this manuscript. (iv) The authors of this work have no disclosures or potential conflicts of interest related to this study. B.S.L.: Consultant and speaker’s bureau for Zim Vie Tether and receives royalties. J.M.P.: Consultant for ZimVie. A.A.: Consultant for Zimvie and receives royalties. L.C.B.: PATENTS (1) Kunes; Brian; (Washington, DC); Hollins; Stacy; (New Castle, VA); Blakemore; Laurel; (Falls Church, VA); Hsu; Brian; (Greenwich, AU); Ferguson; John; (Auckland, NZ). Anterior tether tensioner. US Patent Application 17/091773, filed November 6, 2020. (2) Blakemore, Laurel (Williston, FL) Ross, Catherine(Arlington, VA). Tethering Screw System. US Patent 10,548,639. Filed April 25, 2016, issued February 4, 2020. P.O.N.: ZimVie through Setting Scoliosis Straight Foundation—Research support. A.F.S.: Zim Vie—IP royalties and paid consultant. L.L.H.: Zimmer: Paid presenter or speaker. S.A.S.: Globus Medical Royalties. The remaining authors declare no conflicts of interest., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)