IMPORTANCE: Glaucoma-related adverse events constitute major sight-threatening complications of cataract removal in infancy, yet their relationship to aphakia vs primary intraocular lens (IOL) implantation remains unsettled. OBJECTIVE:To identify and characterize cases of glaucoma and glaucoma-related adverse events (glaucoma + glaucoma suspect) among children in the Infant Aphakia Treatment Study by the age of 5 years. DESIGN, SETTING, AND PARTICIPANTS:A multicenter randomized clinical trial of 114 infants with unilateral congenital cataract in referral centers who were between ages 1 and 6 months at surgery. Mean follow-up was 4.8 years. This secondary analysis was conducted from December 23, 2004, to November 13, 2013. INTERVENTIONS:Participants were randomized at cataract surgery to either primary IOL or no IOL implantation (contact lens). Standardized definitions of glaucoma and glaucoma suspect were created for the Infant Aphakia Treatment Study and applied for surveillance and diagnosis. MAIN OUTCOMES AND MEASURES:Development of glaucoma and glaucoma + glaucoma suspect in operated on eyes for children up to age 5 years, plus intraocular pressure, visual acuity, and axial length at age 5 years. RESULTS:Product limit estimates of the risk for glaucoma and glaucoma + glaucoma suspect at 4.8 years after surgery were 17%(95%CI, 11%-25%) and 31% (95%CI, 24%-41%), respectively. The contact lens and IOL groups were not significantly different for either outcome: glaucoma (hazard ratio [HR], 0.8; 95%CI, 0.3-2.0; P = .62) and glaucoma + glaucoma suspect (HR, 1.3; 95%CI, 0.6-2.5; P = .58). Younger (vs older) age at surgery conferred an increased risk for glaucoma (26%vs 9%, respectively) at 4.8 years after surgery (HR, 3.2; 95%CI, 1.2-8.3), and smaller (vs larger) corneal diameter showed an increased risk for glaucoma + glaucoma suspect (HR, 2.5; 95%CI, 1.3-5.0). Age and corneal diameter were significantly positively correlated. Glaucoma was predominantly open angle (19 of 20 cases, 95%), most eyes received medication (19 of 20, 95%), and 8 of 20 eyes (40%) underwent surgery. CONCLUSIONS AND RELEVANCE:These results suggest that glaucoma-related adverse events are common and increase between ages 1 and 5 years in infants after unilateral cataract removal at 1 to 6 months of age; primary IOL placement does not mitigate their risk but surgery at a younger age increases the risk. Longer follow-up of these children may further characterize risk factors, long-term outcomes, potential differences between eyes having primary IOL vs aphakia, and optimal timing of unilateral congenital cataract removal. TRIAL REGISTRATION:clinicaltrials.gov Identifier: NCT00212134.