X-linked adrenoleukodystrophy is a metabolic disorder with broad clinical variations. The disease may be considered as a differential diagnosis in the case of encephalopathy, polyneuropathy, multiple sclerosis-like syndromes and adrenal insufficiency with unknown etiology. The most common form of adrenoleukodystrophy is lethal and starts with dementia in boys under ten years of age. The genetic defect is located to the Xq28 region and codes for a protein which regulates the transport of beta-oxidation enzymes in the peroxisomes. A defect of this protein seems to cause the accumulation of very long-chain fatty acids. This defect can be measured easily in the serum from patients and female carriers. Therapeutic attempts, for instance with Lorenzo's oil, in order to reduce serum level of very long-chain fatty acids, have not proven to be effective in already neurologically symptomatic patients. At present, the treatment of choice seems to be bone marrow transplantation in presymptomatic boys.