To compare the intraocular pressure (IOP)-lowering efficiency of gonioscopy-assisted transluminal trabeculotomy (GATT) and trabeculectomy (TRAB) with mitomycin C in patients with primary open-angle glaucoma (POAG) and pseudoexfoliative glaucoma (PEXG). In this retrospective comparative study, consecutive patients with POAG or PEXG who underwent GATT or TRAB by a single surgeon and with a follow-up period of at least 1 year were included. Surgical success rates, change in best-corrected visual acuity, IOP, the need for antiglaucoma medication, surgical complications, and the need for additional glaucoma surgery were compared. Surgical success was defined as an IOP reduction of ≥30% or an IOP of ≤18 mmHg. Complete success was defined as without medication. Qualified success was defined as with or without topical medication. The mean baseline IOP was 27.4 ± 8.3 and 24.6 ± 7.6 mmHg (P = 0.13) with the mean number of medications being 3.7 ± 1.0 and 3.7 ± 1.1 (P = 0.98) in TRAB and GATT, respectively. At 12 months, the mean IOP was 15.3 ± 3.5 and 12.5 ± 4.6 mmHg (P = 0.24) with the mean number of medications being 0.9 ± 1.2 and 0.8 ± 1.4 (P = 0.76) after GATT and TRAB, respectively. IOP was lowered from baseline by 52.7% ± 17.5% after TRAB and 45.7% ±18.6% after GATT (P = 0.12). There was no decrease in best-corrected visual acuity in either group. The qualified surgical success rate was 94.4% in the GATT group and 94.9% in the TRAB group (P = 0.75). Percentage of complete success was 64.1% and 52.8% (P = 0.22) after TRAB and GATT, respectively. In patients with POAG and PEXG, GATT was as effective and safe as TRAB in lowering IOP and reducing the number of antiglaucomatous drugs.