Trichothiodystrophy (brittle sulfur-deficient hair) is a marker for several autosomal recessive neurocutaneous syndromes with neurological manifestations and mental retardation. In Tay syndrome, the trichothiodystrophy is accompanied by congenital ichthyosis, short stature, delayed physical and mental development and pyramidal tract signs with increase in muscular tone and brisk tendon reflexes. The pathogenesis of these neurological manifestations is not fully elucidated. We present a case of Tay syndrome in which a cranial MRI revealed an almost total lack of myelin within the cerebral hemispheres and a patchy hypomyelination of the cerebellum. In accordance, a strongly prolonged visual evoked response pointed to a dysfunction of the white matter in Tay syndrome.