To identify risk factors for surgical failure after gonioscopy-assisted transluminal trabeculotomy (GATT) in juvenile open-angle glaucoma (JOAG).Prospective, interventional case series.GATT was the initial surgery in 70 eyes of 70 patients with JOAG. Surgical success was defined as a postoperative intraocular pressure (IOP) of ≤21 mm Hg with at least a 20% reduction from preoperative IOP, with or without the use of antiglaucoma medication (qualified and complete success, respectively) at each postoperative visit. IOP spike was defined as IOP >30 mm Hg and an increase of at least 10 mm Hg from IOP before the spike, and then reduced to ≤21 mm Hg.The median age at the time of surgery was 19.3 years (range, 4.9-37.5 years) with a visual field mean deviation of -17.4 ± 10.6 dB. Mean IOP decreased from 31.3 ± 9.5 mm Hg preoperatively to 15.8 ± 2.7 at 12 months postoperatively. The complete and qualified success rates were 74.3% and 91.4%, respectively. An IOP spike occurred in 52 eyes (74%), with a median spike duration of 3.5 days (range, 1-21 days). Longer duration of IOP spike (P = .009) and older age at the time of surgery (P = .025) were both associated with worse surgical outcomes. Advanced disease was associated with prolonged IOP spike (P = .007).GATT provided excellent outcomes in patients with severe JOAG. Older age and longer duration of postoperative IOP spike are risk factors for failure. Severe cases are more likely to have longer durations of IOP spike. Frequent IOP monitoring during the early postoperative period is needed to detect IOP spikes in these patients.Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.