Purpose To report the outcomes of gonioscopy-assisted transluminal trabeculotomy (GATT) for juvenile-onset primary open-angle glaucoma (JOAG). Methods A consecutive case series of JOAG patients who underwent GATT was reviewed with follow-up period of up to 18 months. Intraocular pressure (IOP), number of glaucoma medications and success rate were compared between eyes with and without prior glaucoma surgery, and between mild-to-moderate and severe cases defined based on Humphrey Visual Field mean deviation. Results In total, 59 eyes of 48 patients were included. Overall, IOP was reduced from 26.5 +/- 9.0 mmHg on 3.7 +/- 0.9 medications preoperatively to 14.7 +/- 3.0 mmHg on 0.7 +/- 1.2 medications at 12 months and to 14.1 +/- 2.3 mmHg on 0.4 +/- 0.8 medications at 18 months postoperatively (P < 0.001). The complete and qualified success rates were 70.8% and 81.2% at 12 months, and 58.6% and 81.2% at 18 months, respectively. Eyes with and without prior glaucoma surgery did not differ significantly in terms of postoperative IOP, glaucoma medication and success rate. In addition, GATT was effective for both mild-to-moderate and severe cases; the latter achieved a surgical success of 79.1%. Conclusions GATT is effective for JOAG. In particular, this case series suggests that GATT is promising in treating severe JOAG and those with prior glaucoma surgery.