Hou Y, Allen T, Wolters PL, et al. - This is the first longitudinal study describing the cognitive development of children with neurofibromatosis type 1 (NF1) and plexiform neurofibromas and identifying predictors of cognitive development. The sample consisted of 88 children with NF1 and plexiform neurofibromas (aged 6–18y, mean = 12y, SD = 3y 7 mo) on a natural history study at the National Cancer Institute. Neuropsychological evaluations (eg, IQ, academic achievement, attention, and executive functioning) have been administered three times over 6 years. The total sample of children with NF1 and plexiform neurofibromas, relative to normative peers, showed significantly lower scores in most cognitive domains and decreased z-scores over time in math, writing, inhibitory control, and working memory. Children who had parents with (vs without) NF1 were more likely to experience decreased z-scores in performance IQ, reading, writing, attention, and working memory. Findings suggested an association of higher (vs lower) parental education with higher levels of IQ, math, reading, and cognitive flexibility and a slower reduction in math z-scores. Children’s gender and the number of NF1 disease-related complications were not associated with most cognitive outcomes. Children with NF1 and plexiform neurofibromas are at high risk of cognitive difficulties and decreasing z-scores over time in different domains of cognitive function. The results illustrate the need for a better understanding of these children's variations within-group and their need for individualized educational plans.