PURPOSE: To evaluate ultrasound biomicroscopy (UBM) characteristics of trabeculodysgenesis and explore its correlation with the outcomes of microcatheter-assisted trabeculotomy (MAT) in eyes with primary congenital glaucoma (PCG). DESIGN: A prospective, interventional case series. METHODS: Patients with newly diagnosed PCG were consecutively recruited, and subsequently MAT was tried as their first glaucoma surgery. All participants underwent UBM prior to surgery. The trabeculodysgenesis was classified into 3 types according to the severity of the anterior insertion of iris and ciliary processes (type 1, severe trabeculodysgenesis; type 2, moderate trabeculodysgenesis; type 3, mild trabeculodysgenesis). Surgical success was defined as a postoperative intraocular pressure of <= 21 mm Hg with at least a 30% reduction from preoperative intraocular pressure without additional medical or surgical therapy, and with decreased corneal edema, stabilized corneal diameter, and no additional optic nerve damage for at least 6 months after surgery. RESULTS: MAT was tried on 49 eyes with PCG (33 patients) as the first glaucoma surgery. The ratios of the type of trabeculodysgenesis (type 1: type 2: type 3) were 1:1:1.7 among eyes. In multivariate analysis, age (at the time of operation) (P < .001) and sex (P = .002) were factors associated with the type of trabeculodysgenesis. At 24-month follow-up, type 1 achieved a 57.1% surgical success rate, type 2 achieved 70.5%, and type 3 achieved 95.5% (P=.022). Severe trabeculodysgenesis (P=.014), as well as poorer corneal trans-parency (P = .037), was associated with worse surgical outcome. CONCLUSIONS: UBM grading of trabeculodysgenesis in PCG is helpful for MAT prognosis. Combined with preoperative corneal opacity score, it may be used to predict the outcome of MAT surgery. (C) 2018 Elsevier Inc. All rights reserved.