PURPOSE: To analyze the long-term results of ab externo trabeculotomy with a Harms trabeculotome at a single, tertiary care pediatric hospital. METHODS: The medical records of pediatric patients operated on between September 2006 and June 2018 were reviewed retrospectively. Kaplan-Meier analysis was performed, with success defined as postoperative intraocular pressure (IOP) of =21 mm Hg, >20% reduction from preoperative IOP, and no need for further glaucoma surgery. Risk factors for failure were identified using Cox proportional hazards ratio. RESULTS: A total of 63 eyes of 40 patients were included. The cumulative probability of success rate was 83% at 3 months, 76% at 6, 73% at 12, 72% at 18, and 65% at final visit. Presentation within 3 months of life was associated with a less favorable outcome. Thirty-five eyes (56%) underwent repeat trabeculotomy to treat a different area of the trabecular meshwork because of inadequately controlled IOP after the first session. Of those who needed another session of trabeculotomy, the final success rate was 60.2%. IOP significantly decreased from 29.79 +/- 7.67 mm Hg at baseline to 16.13 +/- 3.41 mm Hg by final follow-up (P = 0.001). Patients were followed for an average of 85.74 +/- 32.95 months. IOP and success rates remained stable 18 months after surgery. CONCLUSIONS: In our patient cohort, ab externo trabeculotomy was associated with good long-term results. More extensive trabeculotomy (ie, more than one procedure) was associated with better long-term success rates.