The impact of magnetic resonance imaging (MRI)-identified T2-weighted hyperintensities (unidentified bright objects) on the cognitive function of children with neurofibromatosis 1 is controversial. We recruited 32 right-handed children with neurofibromatosis 1 (22 boys, 10 girls) aged between 5 and 16 years (mean age 10.2 years) for magnetic resonance imaging examinations and neuropsychologic evaluation. Statistical analysis was performed to evaluate the significance of the hyperintensities. Twenty-four children had unidentified bright objects, whereas eight children did not. Using the t-test, thalamic lesions were associated with lower intellectual function (P = .031). Left globus pallidus hyperintensities were associated with a lower attention score (P = .04), and right middle cerebellar peduncle hyperintensities were associated with a lower sensorimotor score (P = .05). The size of the thalamic lesions correlated with cognitive function (P < .05). Among the group with unidentified bright objects, there was a significant association between more involved sites on the dominant hemisphere and impaired verbal function (r = -.55; P = .005). Unidentified bright objects in the thalamus, globus pallidus, and middle cerebellar peduncles and the laterality of the lesions had an impact on cognitive function.