A major neurological deterioration, beginning with ataxia, led to the diagnosis of familial vitamin E deficiency in a girl. Based upon vitamin E determinations, 4/8 members of the (consanguineous) sibship were considered to be homozygous. Homozygosity was also found for the alleles of six markers linked to the AVED locus, recently identified in similar Tunisian or Sicilian families on chromosome 8q. Measures of vitamin E in lipoprotein fractions and in liver biopsy after vitamin E oral load suggested that free diffusion of vitamin E between the different compartments was possible and even increased. However, a high-affinity ligand seemed to be lacking, either in the hepatic recycling of vitamin E or in both the hepatic and the other vitamin E compartments. The 5-year substitutive treatment was successful only in the pre- or paucisymptomatic patients. Serum vitamin E must be measured in any unexplained progressive ataxia.