Objectives: To report the incidence of glaucoma and glaucoma suspects in the IATS, and to evaluate risk factors for the development of a glaucoma-related adverse event in patients in the IATS in the first year of follow-up. Methods: A total of 114 infants between 1 and 6 months of age with a unilateral congenital cataract were assigned to undergo cataract surgery either with or without an intraocular lens implant. Standardized definitions of glaucoma and glaucoma suspect were created and used in the IATS. Results: Of these 114 patients, 10 (9%) developed glaucoma and 4 (4%) had glaucoma suspect, for a total of 14 patients (12%) with a glaucoma-related adverse event in the treated eye through the first year of follow-up. Of the 57patients who underwent lensectomy and anterior vitrectomy, 5 (9%) developed a glaucoma-related adverse event; of the 57 patients who underwent an intraocular lens implant, 9 (16%) developed a glaucoma-related adverse event. The odds of developing a glaucoma-related adverse event were 3.1 times higher for a child with persistent fetal vasculature and 1.6 times higher for each month of age younger at cataract surgery. Conclusions: Modern surgical techniques do not eliminate the early development of glaucoma following congenital cataract surgery with or without an intraocular lens implant. Younger patients with or without persistent fetal vasculature seem more likely to develop a glaucoma- related adverse event in the first year of followup. Vigilance for the early development of glaucoma is needed following congenital cataract surgery, especially when surgery is performed during early infancy or for a child with persistent fetal vasculature. Five-year follow- up data for the IATS will likely reveal more glaucomarelated adverse events. Trial Registration: clinicaltrials.gov Identifier: NCT00212134.