This unicentric randomized clinical trial was designed to compare the surgical outcomes of mitomycin C-enhanced trabeculectomy (MMC-TRAB) with and without subtenon triamcinolone acetonide (TAAC) injection in patients with non-inflammatory glaucomas. This trial is registered at the Brazilian Registry of Clinical Trials (ReBEC) under the register number RBR-53f8nh. Consecutive non-inflammatory glaucoma patients requiring surgical intervention were randomized into two groups. In the control group, eyes underwent standard MMC-TRAB, while in the intervention group, besides the standard MMC-TRAB, these eyes also received a subtenon TAAC injection (4mg) close to the bleb site at the end of the surgery. The main outcomes of the study were surgical success rates, intraocular pressure (IOP) and number of medications at all timepoints. Success was defined as IOP ≤ 15 mmHg and subdivided in complete or qualified according to the need of medication. A total of 75 eyes of 63 different patients were included (intervention group = 39 eyes; control group = 36 eyes). There was no difference between groups at baseline (p>0.11). Multivariable regression analysis indicated that IOP levels were significantly lower in the intervention group at 18 and 24 months of follow-up when number of medications was considered as a covariate (P<0.001). Complete success rates were higher in the intervention group at 06 (90.9% vs 68.7%; p = 0.03), 12 (87.2% vs 66.7%; p = 0.02) and 18 months (87.2% vs 66.7%; p = 0.02). Additionally, although success rates at 24 months were higher in the intervention group (82.0% vs 66.7%; p = 0.09), this difference did not reach statistical significance. Qualified success rates did not significantly differ between groups at all timepoints. In conclusion, this study found significantly lower IOPs levels at 18 and 24 months of follow-up and higher complete success rates until 18 months of follow-up, with the use of subtenon TAAC as an adjuvant to standard MMC-TRABs in non-inflammatory glaucoma patients.