PurposeTo describe the frequency, characteristics, and treatment outcome of persistent fetal vasculature (PFV) in children undergoing surgery for congenital and infantile cataract in the first 2 years of life.Patients and methodsObservational population-based cohort study with case identification through active surveillance and standardised data collection via a national clinical network, the British Isles Congenital Cataract Interest Group (BCCIG).ResultsThe IoLunder2 cohort comprises 246 children undergoing surgery for bilateral and unilateral congenital and infantile cataract in the first 2 years of life. A total of 58/246 (24%) children had PFV (%): overall, 46/95 (46%) with unilateral cataract, and 12/141 (8%) with bilateral disease. Anterior segment vascular remnants were more common in bilateral than unilateral disease (75 vs 11%, P=0.01). At 1 year after surgery, 20% of children with bilateral PFV and 24% with unilateral had achieved normal vision for age within the operated eye. The prevalence of post-operative glaucoma was 9% (of children with bilateral disease) and 4% (unilateral).ConclusionPFV is significantly more common than previously reported, and outcomes are comparable to that for congenital and infantile cataract overall.