In Sturge-Weber syndrome in neonates, evaluation of the extent of the brain parenchymal involvement is difficult due to the lack of calcification, although it is important for initiation of preventive antiepileptic treatment and prediction of prognosis. We present the first application of diffusion-tensor imaging with fractional anisotropy and ADC maps in a 7-day-old neonate. Abnormal T2 hypointensity in the subcortical white matter corresponded to the areas of increased FA and decreased ADC on diffusion-tensor imaging, which probably represents abnormal hypermyelination. Diffusion-tensor imaging enabled to quantify the abnormal hypermyelination, and is useful in early diagnosis of Sturge-Weber syndrome.