In subjects with neurofibromatosis type 1 (NF1), we show that a reduction in the visual field is the most sensitive indicator of gliomas along the optic pathway. Therefore, we conclude that a visual field evaluation is the most sensitive clinical test among those evaluated to predict the presence of optic pathway pathology on an MRI examination. These data may contribute to the establishment of more precise guidelines for the evaluation and treatment of children with NF1.