A 6-year old Turkish boy with a recently defined entity: "leukoencephalopathy with vanishing white matter" is described. He was born to consanguinous parents. His psychomotor development was normal till he first presented with fever and generalized tonic-clonic seizures at the age of 2.5, followed by rapid motor and mental deterioration. Decerebrate posture and marked spasticity subsequently developed. The initial MRI examination showed diffuse involvement of white matter, including subcortical U-fibers, with signal intensity parallel to CSF on all sequences. The white matter appeared swollen. The ventricles were slightly enlarged and there was cavum septi pellucidi et vergae. The posterior crus of the internal capsule, external and extreme capsules were affected. Cerebellar hemispheres and vermis showed atrophy. The involvement pattern of brainstem was noteworthy in that pontine tegmentum and cruri cerebri were affected. Follow-up MRI obtained after three years did not show any interval change. Brain biopsy showed thinned cortex with relatively preserved cortical layering and neuronal structure. There was rarefaction of the white matter with cystic degeneration. Fibrillary gliosis and increased number of oligodendroglial cells were observed within the cerebral white matter.