Background <p>Children with brain tumours often suffer from late diagnosis, impacting cure rates and risk of permanent sequelae. Ophthalmological symptoms are common, and we aimed to investigate the frequency, diagnostic interval, and prognostic value of early-onset ophthalmological brain tumour signs.</p> Methods <p>The study is based on data from national Danish health registries and medical files from hospitals and private ophthalmologists collected from all children diagnosed with a primary brain tumour in Denmark during 2007–2017.</p> Results <p>Among 437 included children, 51.7% (<i>n </i>= 226) had ophthalmological tumour signs prior to diagnosis, and 10.8% (<i>n </i>= 47) had ophthalmological symptoms as their initial tumour manifestation. The most common ophthalmological signs in total before diagnosis were reduced visual acuity (<i>n </i>= 73; 16.7%), diplopia (<i>n </i>= 65; 14.9%), abnormal optic nerve (<i>n </i>= 59; 13.5%), and strabismus (<i>n </i>= 50; 11.4%). The median time from initial symptom onset to diagnosis was 12.6 weeks for all children, 15.9 weeks for those with ophthalmological symptoms as their initial tumour sign (<i>p </i>= 0.28), and 12.5 weeks for those with ophthalmological tumour signs at any time before diagnosis (<i>p </i>= 0.71). Children with ophthalmological signs before diagnosis had a higher risk of death (HR: 2.11; 95% CI: 1.32–3.39; <i>p </i>= 0.002).</p> Conclusions <p>Ophthalmological tumour signs are frequent in children with brain tumours, and the diagnostic interval is long regardless of ophthalmological tumour signs being present or not. Taken together with the higher risk of death in the group with ophthalmological tumour signs, this study emphasises the importance of the ophthalmological assessment to ensure timely diagnosis.</p>