In adrenoleukodystrophy, demyelinization of the cerebral hemispheres is associated with Addison's disease. The condition is hereditary and transmitted as a sex-linked recessive trait. The diagnosis must be considered in male teenagers with deterioration of mental functions, motricity and vision and with a computed tomographic image of white matter hypodensity predominant in the posterior part of the cerebral hemispheres. An accumulation of very long chain fatty acids, and characteristic lamellar cytoplasmic inclusions are the biochemical and ultrastructural markers of the disease. Adrenomyeloneuropathy differs from adrenoleukodystrophy in that it begins during adulthood and produces neurological symptoms, notably progressive spastic paraparesis associated with peripheral neuropathy. Heterozygous women can be identified by measurements of very long chain fatty acids in plasma and fibroblast cultures; they sometimes develop spastic paraparesis. The prenatal diagnosis rests on the determination of very long chain fatty acids in amniotic cells.