Precis: Ab interno (gonioscopy-assisted transluminal trabeculotomy) and ab externo 360-degree suture trabeculotomy (ST) achieved similar success rates for reducing intraocular pressure (IOP) without serious complications threatening visual acuity. Purpose: We aimed to compare the efficacy of ab externo and ab interno 360-degree ST in reducing IOP, decreasing the number of antiglaucoma medications required, and decreasing the rates of intraoperative/postoperative complications in adults with open-angle glaucoma (OAG). Patients and Methods: This retrospective study included 33 eyes of 33 patients who underwent ab externo 360-degree ST (group 1) and 23 eyes of 23 patients who underwent ab interno 360-degree ST for OAG (group 2). We analyzed demographics as well as preoperative and postoperative (1, 3, 6, and 12 mo) data related to IOP, the number of antiglaucoma medications, complications, and surgical success rates. Results: In group 1, the mean IOP was 26.2 +/- 10.4 mm Hg, and the mean number of antiglaucoma medications was 3.2 +/- 1.0 preoperatively, decreasing to 11.2 +/- 3.0 mm Hg and 0.1 +/- 0.4 at 12 months, respectively (P<0.001, <0.001). In group 2, the mean IOP was 28.3 +/- 10.4 mm Hg, and the mean number of antiglaucoma medications was 3.5 +/- 0.9 preoperatively, decreasing to 13.3 +/- 6.5 mm Hg and 0.8 +/- 1.0 at 12 months, respectively (P<0.001, <0.001). Decreases in IOP at 6 and 12 months were similar in groups 1 and 2 (50% vs. 47%, P=0.6; and 51% vs. 49%, P=0.7, respectively). At 12 months, complete and qualified success rates were 88% and 97% for group 1 and 57% and 87% for group 2, respectively. The most common complications in both groups were hyphema and transient IOP spikes. Conclusion: Ab interno 360-degree ST is similar to ab externo 360-degree ST in terms of safety and efficacy in patients with OAG.