Visual field deficits can be a consequence of brain tumor location or treatment. The prevalence of unrecognized visual field deficits in children diagnosed with brain tumors is not known. All children at a single tertiary care pediatric children's hospital diagnosed with a primary brain tumor were tested for visual field deficits by a child neurologist and neuro-ophthalmologist over 16 months. Children with reproducible visual field deficits on two separate occasions were included in the analysis. Patients with optic glioma, craniopharyngioma, or previously known visual field deficits were excluded. Fourteen of 92 (15.2%) children (average 8.9 years, 8 girls) had undiagnosed visual field deficits. Average time between diagnosis of tumor and unrecognized visual field deficit was 3.7 years (range 0-13 years). Unrecognized visual field deficits were not associated with age (P = 0.27) or gender (P = 0.38). Visual field deficits were attributed to direct tumor infiltration (n = 8), postoperative complications (n = 5) and post-radiation edema (n = 1). Deficits included bitemporal hemianopsia (n = 2), homonymous hemianopsia (n = 9), quadrantanopsia (n = 2), and concentric visual field loss (n = 1.) Tumor location included temporal lobe (n = 9), parietal lobe (n = 2), posterior fossa (n = 2), hypothalamic-chiasmatic (n = 2) and multifocal areas (n = 4). Children with temporal lobe tumors were more likely to have unrecognized visual field deficits (P = 0.004). In all 14 patients, visual field deficits were determined by examination only and were not reported by either the patient or caregiver regardless of age. The prevalence of unrecognized visual field deficits in children with brain tumors can be surprisingly high. Serial neuro-ophthalmologic evaluation of children with brain tumors is often required to diagnose a visual field deficit since patient or caregiver reporting may be limited.