A 27-year-old man from Marocco developed a progressive dementia leading within a year to a mutic akinetic state. The course of the disease was also marked by epileptic seizures. MRI revealed diffuse white matter involvement. A frontal white matter brain biopsy was consistent with the diagnosis of orthochromatic leucodystrophy, i.e: presence of sudanophilic lipids and pigmented cells associated with myelin loss. Adult forms of orthochromatic leucodystrophy are very rare. Our case was characterized by a fulminant course.