Two cases of N-acetylaspartic aciduria in siblings are described and compared to the 18 cases already reported. The disease should be considered in childhood when a syndrome of severe encephalopathy with macrocephaly, blindness caused by optic atrophy and diffuse leucodystrophy on CT scan occurs. Urinary organic acids gas chromatography confirms the diagnosis. It is probably inherited as an autosomal recessive trait. Aspartoacylase activity deficiency has been reported and this assay could possibly be used for prenatal diagnosis. Pathogenesis is not clearly understood but N-acetylaspartic acid (NAA) seems to be essential for central nervous system myelination. Clinical and anatomic features of N-acetylaspartic aciduria are very similar to Van Bogaert-Bertrand disease (cerebral spongy degeneration or Canavan disease) but heterogeneity of this disease cannot excluded.